Part I basic knowledge

Chapter 1. measurement

There are two main measurement units of length in the world today. One is the metric system. The measurement units are meter (m), centimeter (CM) and millimeter (mm). They are widely used in Europe, China, Japan and other Southeast Asian regions. The other is the British system. The main unit of measurement is inch, which is equivalent to the market size of China’s old system. It is widely used in the United States, Britain and other European and American countries.
1. Metric measurement: (decimal)
1m =100 cm=1000 mm

2. English Measurement: (base 8)

• 1 inch = 8 English minutes
• 1 inch = 25.4 mm
• 3/8¢¢ ×25.4 = 9.52

3. For products with less than 1/4¢¢ and less, their address diameter is indicated by serial number, such as: 4#, 5#, 6#, 7#, 8#, 10#, 12#

Chapter 2. Thread

1. Screw thread is a kind of shape with uniform helix bulge on the cross section of the outer or inner surface of a solid. It can be divided into three categories according to its structural characteristics and uses.

• 1） Common thread: the tooth shape is triangle, which is used to connect or fasten parts. The common thread can be divided into coarse thread and fine thread according to pitch, and the connection strength of fine thread is higher.
• 2） Transmission thread: trapezoidal, rectangular, saw shaped and triangular.
• 3） Sealing thread: used for sealing connection, mainly pipe thread, taper thread and taper pipe thread.

2. Thread fit grade:
Thread fit is the loose or tight size between screw threads, and the fit grade is the specified combination of deviation and tolerance acting on internal and external threads.
（1） For unified inch screw thread, there are three thread grades for external thread: 1a, 2a and 3a, and three grades for internal thread.
Class 1b, 2b and 3b are all clearance fit. The higher the grade number, the tighter the fit. In English screw threads, the deviation is only specified as class 1a and 2a, Grade 3A is zero, and class 1a and 2a are equal.
The larger the number of grades, the smaller the tolerance, as shown in the figure:

• Grade 1a and 1b, very loose tolerance grade, suitable for tolerance fit of internal and external threads.
• Grade 2a and 2b are the most common thread tolerance grades specified for English series mechanical fasteners.
• Grade 3A and 3b, spin to form the tightest fit, suitable for tight tolerance fasteners, for safety critical design.
• For external threads, there is a fit tolerance for grades 1a and 2a, but not for class 3a. Class 1A tolerances are 50% greater than class 2A tolerances and 75% larger than class 3A tolerances. For internal threads, class 2B tolerances are 30% greater than 2A tolerances. Grade 1b is 50% larger than grade 2B and 75% higher than grade 3B.

（2） There are three kinds of thread grades for external thread: 4h, 6h and 6G, and there are three kinds of thread grades for internal thread: 5h, 6h and 7h. (the precision grade of Japanese standard thread is divided into three levels: I, II and III, and generally it is grade II). In metric thread, the basic deviation of H and H is zero. The basic deviation of G is positive and that of E, F and G is negative. As shown in the figure:

• H is the position of tolerance zone commonly used for internal thread, which is not used as surface coating or extremely thin phosphating layer. The basic deviation of G position is used in special occasions, such as thick coating, which is seldom used.
• G is often used for plating 6-9um thin coating. For example, if the product drawing requires 6h bolt, the 6G tolerance zone is adopted for the thread before plating.
• The best combination of thread matching is H / g, H / h or g / h. for the screw thread of refined fastener such as bolt and nut, 6h / 6G fit is recommended.

（3） Thread marking
（3）The main geometric parameters of mechanical thread are as follows:
1） Major diameter / tooth outer diameter (D, d): it is the imaginary cylinder diameter where the external thread top or internal thread bottom coincide. The major diameter of the thread basically represents the nominal diameter of the thread size.
2） (D 2, D 2): D 2 = D 2 = D (d) – 2x3h / 8, where h is the height of the original triangle:
3） Diameter / base diameter (D1, D1): refers to the diameter of the imaginary cylinder with the top of external thread or internal thread. H = (√ 3 / 2) P = 0.866025p (60o yashanjiao); H = 0.960491p (55o yashanjiao)
4） Screw pitch (P): refers to the axial distance between two corresponding points on the middle diameter line of adjacent teeth or the distance between adjacent teeth or two adjacent teeth valleys.

In English system, the number of teeth per inch (25.4 mm) is used to indicate the pitch (table below).

Specifications	Distance between teeth				Specifications	Address path	Number of teeth
	Coarse teeth	Fine teeth		Very fine teeth			Coarse teeth		Fine teeth	Webster’s tooth
M3	0.5	0.35			4#	2.9	40		48
M4	0.7	0.5			6#	3.5	32		40
M5	0.8	0.5			8#	4.2	32		36
M6	1.0	0.75			10#	4.8	24		32
M7	1.0	0.75			12#	5.5	24		28
M8	1.25	1.0		0.75	1/4	6.35	20		28	20
M10	1.5	1.25		1.0	5/16	7.94	18		24	18
M12	1.75	1.5		1.25	3/8	9.53	16		24	16
M14	2.0	1.5		1.0	7/16	11.11	14		20	14
M16	2.0	1.5		1.0	1/2	12.7	13		20	12
M18	2.5		2.0	1.5	9/16	14.29	12		18	12
M20	2.5		2.0	1.5	5/8	15.86	11		18	11
M22	2.5		2.0	1.5	3/4	19.05	10		16	10
M24	3.0		2.0	1.5	7/8	22.23	9		14	9
M27	3.0		2.0	1.5	1	25.40	8		12	8
M30	3.5		3.0	2.0

5） The profile half angle (α / 2): the angle between the tooth side and the vertical line of the thread axis. The half angle of the common thread is 60o / 2, and that of the Webster thread is 55o / 2. Generally speaking, the angle of the screw tooth is 60 o and the angle of the tail tip is 60 o.
6） Thread turning length: it refers to the length of two-phase matching thread and the length of mutually rotating parts along the thread axis direction.
（4）The main geometric parameters of self tapping and self drilling thread are as follows:

• The major diameter / tooth diameter (D1) is the imaginary cylinder diameter of the overlap of the screw crown. The major diameter of the thread basically represents the nominal diameter of the thread size.
• Minor diameter / tooth base diameter (D2): it is the imaginary cylinder diameter with the thread base overlapping.
• Tooth distance (P): it is the axial distance between two points corresponding to the middle meridian line of adjacent teeth. In English, the number of teeth per inch (4mm) is used to indicate the pitch.

The following table lists the common specifications of pitch (Metric) teeth number (British system)
1). Metric self tapping:

Specifications	S T 1.5	S T 1.9	S T 2.2	S T 2.6	S T 2.9	S T 3.3	S T 3.5	S T 3.9	S T 4.2	S T 4.8	S T 5.5	S T 6.3	S T 8.0	S T 9.5
Distance between teeth	0.5	0.6	0.8	0.9	1.1	1.3	1.3	1.3	1.4	1.6	1.8	1.8	2.1	2.1

2). British self tapping:

Specifications		4#	5#	6#	7#	8#	10#	12#	14#
Number of teeth	AB teeth	24	20	20	19	18	16	14	14
	A teeth	24	20	18	16	15	12	11	10

3). Japanese standard wallboard nails:

Specifications		6#	7#	8#	10#
Coarse teeth	Number of teeth	9	9	9	8
	Distance between teeth	2.82	2.82	2.82	3.18
Fine teeth	Number of teeth	18	16	15	12
	Distance between teeth	1.41	1.59	1.69	2.11

4). Mechanical screw (mechanical tooth)

Specifications	Metric system（Distance between teeth）							British system (Number of teeth)
	M2.5	M3	M3.5	M4	M5	M6	M8	4#	5#	6#	8#	10#	12#	1/4
Coarse teeth	0.45	0.5	0.6	0.7	0.8	1.0	1.2	40	40	32	32	24	24	20
Fine teeth	0.35	0.35	0.35	0.5	0.5	0.75	1.0	48	44	40	36	32	28	28

5). Drilling tail screw: there are CSD (mechanical teeth) and BSD (self tapping AB thread) two kinds of drilling screws. The pitch or number of teeth can be referred to mechanical screw (CSD tooth) and self tapping screw (BSD tooth).
（5） The angle of cusp and the angle of tail tip: the angle between the tooth side and the side of tooth is the angle between the tooth side and the tooth side, and the angle of the tail tip is the angle at the end of the thread.

• 1. Self tapping: the cusp angle was 60O and the tip angle was 45O ± 5O.
• 2. Wallboard nail: the angle of tooth hill is 60O, and the angle of tail tip is 25O± 3O.
• 3. The angle of cusp was 40O ± 3O and the angle of tail tip was 25O ± 3O or 34O ± 3O (customer’s special requirements).
• 4. Drill tail screw: the angle of tooth hill is 60O ± 5O. the tail pin of different models is selected for different specifications of products. The main geometric parameters of tail clamping are tail diameter and extension.

Chapter 3. materials

1、 At present, the standard parts in the market are mainly made of carbon steel, stainless steel and copper.
（1） Carbon steel. We distinguish low carbon steel, medium carbon steel, high carbon steel and alloy steel by carbon content in carbon steel.

• 1. Low carbon steel C% ≤ 0.25% is usually called A3 steel in China. It is called 1008101510181022 in foreign countries. It is mainly used for grade 4.8 bolts, grade 4 nuts, small screws and other products without hardness requirements. (Note: the drill tail nail is mainly made of 1022 material.)
• 2. Medium carbon steel 0.25% < C% ≤ 0.45% is usually called No.35 and No.45 steel in China, and it is basically called 1035, ch38f, 1039, 40ACr, etc. in foreign countries. It is mainly used for Grade 8 nuts, grade 8.8 bolts and grade 8.8 hexagon products.
• 3. High carbon steel C% > 0.45%. At present, it is basically not used in the market
• 4. Alloy steel: adding alloy elements to ordinary carbon steel, increasing some special properties of steel, such as 35, 40 Cr Mo, SCM435, 10b38. The main components of Pan Wo screw are C, Si, Mn, P, s, Cr and mo.

（2） Stainless steel. Performance level: 45, 50, 60, 70, 80
Austenite (18% Cr, 8% Ni) has good heat resistance, corrosion resistance and weldability. A1, A2, A4 martensite and 13% Cr have poor corrosion resistance, high strength and good wear resistance. C1, C2, C4 ferritic stainless steel. The forging property of 18% Cr is better than that of martensite. At present, the imported materials on the market are mainly Japanese products. According to SUS304 and SUS304.
（3） Copper. The common material is brass Zinc copper alloy. H62, H65 and H68 copper are used as standard parts in the market.
2、 Pan element used for carbon steel products:

Serial number	Type	Available materials
1	Grade 4.8 hexagon bolt	1008K 1010 1015K
2	Grade 6.8 hexagon bolt	1032 1035 1040 CH38F 1039
3	Grade 8.8 hexagon bolt	1035ACR(M10以下)1040ACR（M12 above）CH38F 1045ACR 1039 10B21 10B33 10B38
4	Grade 8.8 hexagon socket bolt	CH38F 1039 10B21（M10-M12） 10B33 （M14）10B38（M12-M24）10B21
5	Grade 10.9 hexagon bolt	1045ACR   10B38
6	Grade │8│ nuts	1008K 1010
7	Grade 8 nuts	1015(M<16) CH38F (M≥16)
8	Grade 10 nuts	CH38F 1039 10B21 10B33
9	Grade 12 nuts	1039 10B21 10B33 10B38
10	Carriage Bolts	1008 1010 1015
11	Hexagon flange bolt	CH38F 1039 10B21 10B33 10B38
12	Hexagon wood screw	1008K  1010
13	Self tapping screw, wallboard nail, drill tail nail and splint nail	1018  1022  CH22A
14	Machine screw, furniture screw	1008  1010

3、 Influence of various elements in materials on properties of steel:

• 1. Carbon (c): improve the strength of steel parts, especially its heat treatment properties, but with the increase of carbon content, plasticity and toughness decrease, and will affect the cold heading performance and welding performance of steel parts.
• 2. Manganese (MN): to improve the strength of steel parts, and to a certain extent improve the hardenability. In other words, the strength of hardening infiltration is increased during quenching, and the surface quality can be improved by manganese, but too much manganese is unfavorable to ductility and weldability. And it will affect the control of plating.
• 3. Nickel (Ni): improve the strength of steel parts, improve the toughness at low temperature, improve the atmospheric corrosion resistance, and ensure stable heat treatment effect, reduce the effect of hydrogen embrittlement.
• 4. Chromium (CR): it can improve the hardenability, wear resistance, corrosion resistance and strength at high temperature.
• 5. Molybdenum (MO): it can help to control the hardenability, reduce the sensitivity of steel to temper brittleness, and has a great influence on improving the tensile strength at high temperature.
• 6. Boron (b): improves hardenability and contributes to the desired reaction of mild steel to heat treatment.
• 7. Alum (V): refine austenite grain and improve toughness.
• 8. Silicon (SI): to ensure the strength of steel parts, appropriate content can improve the plasticity and toughness of steel parts.

4、 Brief introduction to the properties of stainless steel (304, 316)
The three materials are 300 series austenitic stainless steel, and their chemical compositions are as follows:

Name	C	Si	Mn	P	S	Ni	Cr	Mo	Cu
304M	≤0.06	≤1.0	≤2.0	≤0.045	≤0.03	8.91-10.0	18.0-20.0	0	0
316	≤0.03-0.06	≤1.0	≤2.0	≤0.045	≤0.03	10.0-14.0	16.0-18.0	2.0-3.0	0
304HC	≤0.08	≤1.0	≤2.0	≤0.045	≤0.03	8.0-10.5	17.0-19.0	0	1.0-3.0

The relationship between main chemical composition and properties of stainless steel is as follows
1. Carbon C can increase hardness and strength, but too high content will reduce its ductility and corrosion resistance
2. Chromium and chromium can increase corrosion resistance, oxidation resistance, grain refinement, strength, hardness and wear resistance
3. Ni can increase high temperature strength and corrosion resistance, and reduce the rate of cold work hardening
4. Molybdenum and molybdenum have good corrosion resistance to oxides and seawater
5. Copper and copper are good for cold forming and reduce magnetism

Other properties of materials

1. The above materials are normal and non-magnetic. After cold working, 304m has a little magnetism (about 1.6u-2.0u), 304HC is (about 1.01u-1.6u), and 316 material is less than 1.01u after cold working.
2. All materials have good ductility, easy to cold processing, tensile strength, yield strength, can meet the requirements. (TS tensile strength min 700n / mm, ys yield strength min 450N / mm)

Conclusion

1. 304m, 304HC and 316 are the most widely used materials of 300 series austenitic stainless steel. The magnetic properties of the materials after cold working are 316 < 304HC < 304m. 316 material has better chemical resistance, pitting corrosion resistance and seawater corrosion resistance than 304m and 304HC.
2. In a word, the characteristics of stainless steel standard parts are corrosion-resistant, beautiful and hygienic, but their strength and hardness are equivalent to carbon steel (grade 6.8) under normal conditions. Therefore, the stainless steel products shall not be impacted, knocked, and their surface finish and precision shall be maintained. Moreover, the force shall not be applied arbitrarily or too much force shall be applied as carbon steel products The generated steel chips are easy to stick to the nut grade, increase the friction force, and easily lead to locking. However, even if the carbon steel produces iron chips, it will fall down, which is not easy to lock compared with stainless steel.

Part II large screw

Chapter 1. product classification

1、 Product category
（1） Hexagon head bolts
1. The British bolt reference standard is ANSI / ASME b18.2.1, and the Japanese standard is JIS b1180. Bsw916 (Wechsler teeth) was used as reference.

• (1) Hex machine bolt: hexagonal bolt without Huasi, with bundle tail and half tooth;
• (2) Hex tap bolt: no Huasi, no bundle tail, full tooth hexagon bolt;
• (3) Hex Cap Screws: with Huasi, with bundle tail and half tooth hexagon bolt.

2. The reference standards for metric bolts are as follows, and their differences are shown in the table:

Old national standard	New national standard	ISO standard	DIN (German standard)
GB30	GB5780(Half tooth) GB5781(Whole tooth) GB5782(Half tooth) GB5783(Whole tooth)	ISO4016 ISO4018 ISO4014 ISO4017	DIN601 DIN558 DIN931 DIN933

（2） Carriage bolts / carriage bolts: ANSI/ASME B18.5, DIN603, ISO 8677, GB12, GB14
（3） Hexagon socket head cap screws: DIN912, GB70, ISO4762, ANSI /ASME B18.3
（4） Hexagon head lag screws: ANSI/ASME  B18.2.1, DIN 571
（5） Furniture screws: according to customer standards
（6） Hexagon flange bolt: IFI 111, GB 5787, DIN 921
2、 Product identification

（1） Drawing of bolt parts:

（2） Identification of bolts:

3、 Sign, performance level
(1) , logo. Hexagon head bolts and screws (thread diameter ≥ 5mm). It is necessary to mark the head with convex or concave characters on the top surface or concave characters on the side of the head. Including performance grade and factory standard. Carbon steel: strength grade mark code consists of two parts separated by “·”. The meaning of the number before “·” in the mark code indicates the nominal tensile strength, for example, “4” of grade 4.8 represents 1 / 100 of the nominal tensile strength of 400N / mm2. The meaning of “·” and the number after the point indicates the yield ratio, that is, the ratio of nominal yield point or nominal yield strength to nominal tensile strength. For example, the yield point of grade 4.8 product is 320 n / mm2. The strength grade mark of stainless steel products is composed of two parts separated by “-“. The symbol before “-” in the sign code indicates the material. For example, A2, A4 and other signs indicate strength after “-“, such as A2-70
(2) Grade. Carbon steel: the mechanical property grade of metric bolt can be divided into 10 performance levels: 3.6, 4.6, 4.8, 5.6, 5.8, 6.8, 8.8, 9.8, 10.9 and 12.9. Stainless steel is divided into three types: 60, 70, 80 (austenite); 50, 70, 80110 (martensite); 45, 60 (ferrite).

Chapter 2. technological process

1、 Production process:

（1） Coil iron:
1. The price element refers to the original wire rod purchased by the manufacturer. A price element mainly includes the following parameters:

• A. Brand
• B. Product name
• C. Specifications
• D. Material
• E. Heat number or batch number
• F. Quantity / weight

2. The main chemical components in steel are: C, Mn, P, s, Si, Cu, al. The lower the content of Al and Cu, the better.
（2） Annealing: eliminate the internal stress in wire processing and increase its forging ability.
（3） Acid pickling: remove a layer of oxide film on the surface of wire rod and lubricate the surface of wire rod to facilitate wire drawing.
（4） Wire drawing: in order to achieve the wire diameter we need.
（5） Head (forming) and tooth rolling: complete the product shape and shape the tooth shape.
（6） Heat treatment: change the mechanical properties of screws.
（7） Electroplating: in order to meet the customer’s requirements for surface treatment, but also can increase some properties of screws. Such as rust, beautiful, etc.
（8） Packaging: pack the products into boxes / boxes according to the standards or customer requirements.
（9） See Part V for the above procedures.

Part III small screw

Chapter 1. product classification

1、 Product category:
（1） Tapping screws
1. Reference standards: British self tapping screw reference standard is ANSI / ASME b18.6.4, metric reference standards are gb845 (R +), gb846 (F +), gb847 (O +), JIS b1115 (-), jisb1122 (+) jisb 1126 (HW), jisb1127 (HF), JIS b1125 、DIN7971、DIN7972、DIN7973、DIN7981、DIN7982、DIN7983、ISO1479（H）、ISO1481（B-）、ISO1482（F-）、ISO1483（O-）、ISO7049（P+）、ISO7050（F+）、ISO7051（O+）。
2. Head type: there are three kinds of head types in the new and old national standards: round head (R), countersunk head (f) and semi countersunk head (o) in the old national standard, pan head (P), countersunk head (f) and semi countersunk head (o) in the new national standard, and various head types are available for British self tapping screws. At present, the common head types of self tapping screws are as follows:

3. Tooth type: at present, there are a, AB, B, BT, BP / BF, C, D, t and other tooth types of self tapping screw, as shown in the figure. Refer to: U.S.A. Fastener standard (original) page 13.

4. The differences between ab teeth and a teeth were as follows

• ① The new version of IFI standard has eliminated a tooth products, but some enterprises are also producing a-tooth products because of the market demand. The main difference between tooth a and tooth AB lies in the number of teeth (as shown in Table 1).
• ② The outer diameter and base diameter of teeth a and ab are also different (as shown in Table 2).
• ③ The head size of 14 ා a tooth and ab tooth of pan head are different (as shown in Table 3), while the basic dimensions of other specifications are the same.

Table 1

Specifications		4#	5#	6#	7#	8#	10#	12#	14#
Number of teeth	AB teeth	24	20	20	19	18	16	14	14
	A teeth	24	20	18	16	15	12	11	10

Table 2

Specifications				4#	5#	6#	7#	8#	10#	12#	14#
Tooth diameter	AB teeth	Lower limit		2.79	3.20	3.43	3.79	4.09	4.65	5.13	6.10
		upper limit		2.90	3.30	3.53	3.91	4.22	4.80	5.46	6.25
	A teeth		Lower limit	2.79	3.20	3.45	3.86	4.11	4.78	5.46	6.30
			upper limit	2.90	3.30	3.58	4.01	4.27	4.93	5.61	6.45

Table 3

Test items	Head diameter	Cutting groove head thickness	Depth of trench	Cutting groove width	Crosshead thickness	Cross deep	Cross width
Tooth type
A	11.60-12.09	3.20-3.53	1.72-2.10	1.63-1.90	3.96-4.29	3.00-3.66	6.81-7.1
AB	12.05-12.42	3.34-3.58	1.81-2.13	1.66-1.83	4.15-4.37	3.03-3.58	6.84-7.06

5. Length and tooth length:
(1) Length specification: all the self tapping screws produced by our company are full teeth (according to the standard specified by the customer when required)
(2) Length measurement: for countersunk and semi countersunk head screws, the length should be measured from the end to the top of the head.
(3) Allowable tolerance of length:

• ① The allowable tolerance of AB teeth and BP teeth is ± 0.03in when the nominal length is less than or equal to 1 inch, and ± 0.05in when the length is greater than 1 inch.
• ② For B, BT, C and t teeth, the allowable tolerance of length is – 0.03in when the length is more than 3 / 4 in. When the length is greater than 3 / 4 in to 1-1 / 2 in, the allowable tolerance is – 0.05 in. If the length is greater than 1-1 / 2 inch, the allowable tolerance is – 0.06 in.

(4) Tooth length requirements:
Requirements for AB, B, BP and BT teeth: the complete thread should be processed as close to the head as possible. At the distance y below the head, the small diameter of the thread should be within the specified limit, as shown in the table below.
② If the nominal length is greater than the listed products, the minimum complete thread length shall not be less than the provisions of LT listed in the table below.
Table 4 thread length of AB, B, BF, BP and BT self tapping screws

Nominal size of thread	L	LT	Y
	Nominal length of screw	Full thread length	Unthreaded length under head
		Min（in）	Max（in）
4#	13/16	0.67	0.042
5#	15/16	0.75	0.050
6#	1＂	0.83	0.050
7#	1-1/8	0.91	0.053
8#	1-1/4	0.98	0.056
10#	1-3/8	1.14	0.062
12#	1-5/8	1.30	0.071
1/4	1-13/16	1.50	0.071

（2） Wallboard nail
1. Reference standards: JIS B 1125, GB / T 14210-93c and customer specified standards.
2. Head type: at present, there are horn head (DW), but also large flat head Huasi (TW) and Warwick head (AF).
3. Tooth type:
(1) There are two main types of wallboard nails: fine teeth and coarse teeth. The distance and number of teeth are shown in the table below. Fine teeth are divided into double teeth and double teeth single out and high and low teeth. Generally speaking, the angle of cusp is 60o and the angle of tail tip is 25O± 3O. However, some customers require the angle to be 45O± 5O.

Specifications	Coarse teeth		Fine teeth
	Number of teeth	Distance between teeth	Number of teeth	Distance between teeth
6	9	2.82	18	1.41
7	9	2.82	16	1.59
8	9	2.82	15	1.69
10	8	3.18	12	2.11

(2) Since the wall panel nail (fine tooth) has the requirement of attack speed, and the crack of tail tip, over pointed tail tip, blunt tail and burning of tail tooth may lead to insufficient attack speed. Therefore, the following table is specially made for the attack speed:

Address diameter D	Thrust/KG	Plate thickness/mm	Attack time (max)/S	Speed/rpm
2.9	12	0.6	1.5	2500-3000
3.5	15	1.0±0.10	2.5
3.9			2.5
4.2			3.0
4.8			3.5

4. Length:
(1) For products with a length of more than 3 / 8in, the lower limit of dimensional tolerance is generally taken. If the length L is less than 2 in (50 mm in metric system), they are all full tooth (LT) products. The tooth length is 2 in when the address is 2 in to 3 in long, and 2-1 / 2 when the tooth length is more than 3 in. The tooth length is 2 / 3 of the address length. LT = 2 / 3 × L.
(2) Products with a length of more than 4 in (100 mm in metric system) are easy to bend, so there is a requirement for runout. There are two forms of bending: one is caused by rolling teeth, that is, bending from the first tooth, and the other is caused by heat treatment, that is, the whole arc is formed.
（3） Drilling tail screw
1. Reference standards: ANSI / ASME b18.6.4, DIN7504.
2. At present, the common types of drilling tail screw head are hexagonal Huasi head (HW), pan head (P) and flat head (f).
3. There are mainly BD teeth and CD teeth. The difference between them is that BD teeth are ab teeth in self tapping screws, while CD teeth are mechanical teeth.
4. Length: when the address length is less than 1-1 / 2 in, it is full tooth; when it is more than 1-1 / 2 in, it is half tooth, and the tooth length is 1-1 / 2 in.
5. Introduction to BSD and CSD screws:
(1) The screw of BSD type should have pitch thread and bit end with different shapes. The drill bit is usually No.2 or No.3, and its design is suitable for different plate thickness conditions. When the nominal length is equal to or less than 1.50 inches, all screws are full thread screws. The empty thread under the head, including the thread ending, should be 1 pitch, and if possible, it should be smaller.
(2) CSD screw is a kind of machine screw thread. The combination of its diameter and pitch is similar to the unified thread, and the end of drill bit with different shapes is marked as No. 2 or no. 3. Its design type is suitable for different plate thickness conditions. CSD type screw does not need to accept thread measurement, but should meet the size specified in the standard. Generally, the screw thread ratio of machine screw to pitch thread is used CSD type screw should be used where the nominal length of CSD screw is equal to or less than 1.50in. The screw with the thread blank under the head, including the thread ending, should be one pitch or less.
6. Selection of BSD and CSD screw clamping die:
Under normal conditions, No.2 tail is used for less than 6 × 10, No.3 tail is used for more than 8 × 10, No.2 tail is used when the specification length of 8 × 10 × 10 × is less than 1 / 2 (including) (when the length of flat head is less than 5 / 8 (inclusive), No.2 tail is made, and No.3 tail is made when the length of other 10 × 10 exceeds this specification. In addition, the minimum length required for flat head BSD 2 and 3 tail is as follows:

7. Requirements of screw tapping speed
The main characteristic of the drilling tail screw is penetration. If the diameter of the tool is too small, the surface hardness is too low, and the tail clamping is not good, the attack speed may be insufficient. Saej78 and DIN7504 have the following regulations on attack speed:

Specifications/D	Thrust/Ib （kg）MAX	Plate thickness/inch （mm）	Attack time/（S）Max	Speed/rpm		Specifications/D	Thrust/kg Max	Plate thickness/mm	Attack time/（S） Max	Speed/rpm
4#	30（13）	0.065 ±0.003 (1.65 ±0.07)	2.0	2500		ST2.9	15	0.7+0.7	3	1800- 2500
6#	35（15）		2.5			ST3.5	15	1+1	4
8#	35（15）		3.0			ST3.9	15	1+1	4.5
10#	40（18）		3.5			ST4.2	25	1.5+1.5	5
12#	50（22）		4.0	1800		ST4.8	25	2+2	7
14#	50（22）		4.5			ST5.5	35	2+3	11	1000- 1800
						ST6.3	35	2+3	13

（4） Splint nail
1. Reference standard: customer requirements
2. Head type: at present, the common ones are flat head, pan head and large flat head. The groove type is mostly rice groove and plum blossom groove.
3. Tooth type: the angle of splint nail and Yashan is 400, one side is 250 and the other side is 150, so that the product has a certain self-locking function. The angle of tail tip is 250 ± 30 or 340 ± 30, and the angle of tail tip is 340 ± 30 in general short size. The tooth base of three splint nail is generally smooth without iron filings. Because the product is not smooth, it is difficult to screw the product into the hard wood. At the same time, there will be breakage phenomenon, that is, the screw in test may not meet the requirements. In addition, if there is iron filings, it can not be plated to the substrate during electroplating. When the screw is screwed into the wood, the iron filings will fall off, which makes the matrix easy to corrode and cause the product to rust.
（5） Machine screw:
1. Reference standard:
(1) 85 (GBO) – 9685 (GBO) – 9685 (GBO) – 9685 (GBO) – 9685 (GBO) – 9685 (GBO) – 9685 (GBO) – 9685 (GBO) – 9685 (GBO) – 9685 (GBO) – 9685 (GBO) – 9685 (GBO) – 9685 (GBO) – 9685 (GBO) – 9685 (GBO) – 9685 (GBO) – 9685 (GBO) – 9685 (GBO) – 9685 (GBO) – 9685 (GBO) – 968 (GB0 +), gb6 (GBO) – 9685 (GBO) – 968 (GB0 +), GB0 (gb0-85), gbo-9685 (GB0 +), GB0 (gb0-
(2) British system: ANSI / ASME b18.6.3
2. Head type: like self tapping screw, there are three head types in the new and old national standards, including round head (R), countersunk head (f) and semi countersunk head (o) in the old national standard, and pan head (P), countersunk head and semi countersunk head in the new national standard. The head type of English machine screw is the same as that of British self tapping screw, and there are several head types as follows:

3. Tooth type: the tooth type of the machine screw is the mechanical tooth, and the tooth spacing is listed in the following table:
(1) metric system

Specifications		M2.5	M3	M3.5	M4	M5	M6	M8	M10
Distance between teeth	Coarse teeth	0.45	0.5	0.6	0.7	0.8	1.0	1.25	1.5
	Fine teeth	0.35	0.35	0.35	0.5	0.5	0.75	1	1.25

（2) british system:

Specifications		4#	5#	6#	8#	10#	12#	1/4	5/16	3/8
Distance between teeth	Coarse teeth	40	40	32	32	24	24	20	18	16
	Fine teeth	48	44	40	36	32	28	28	24	24

4. All screws are produced by our company at present.
2、 Product identification:

Chapter 2. technological process

1、 Production process:

1. Self tapping screw (splint screw)

2. Mechanical screw:

3. Drilling tail screw (cutting screw)

Chapter 3. mechanical properties

1、 Requirements for mechanical properties of self tapping screws.
1. Core hardness: standard value hrc28-38, the measured value of our products is about hrc31-33. When testing, take the section 1-2 times the diameter from the tail. If the length of the address is too short, it can be embedded first, and then measure the hardness.
2. Surface hardness: Standard min hv450, the actual measurement of our products is about hv530.
3. Carburized layer: standard 4# – 6#: 0.05-0.18mm, 8# – 12#: 0.10-0.23 mm, 14#: 0.13-0.28 mm.
The main purpose of carburizing is to enhance the surface hardness and ensure the strength of teeth. If decarburization is too deep and carburization is insufficient, the strength of teeth will not meet the requirements, that is, the teeth will be damaged during the screw in test.
4. Torque:

Standard	Specifications	4#	5#	6#	7#	8#	10#	12#	14#
	A tooth	14	21	28	35	45	56	96	145
	AB teeth	14	21	28	35	45	65	102	165

5. Screw in test: screw the self tapping screw into a steel plate with reserved test hole. The self tapping screw shall form a matching thread in the test plate, and the screw thread itself shall not be deformed or damaged until the end taper thread completely passes through the test plate. The screw in test is only applicable to AB, B, BP type self tapping screws. IFI stipulates that the test plate shall be made of semi hard low carbon cold rolled steel, and the hardness of steel plate shall be Rockwell 70 – 85hrb. The standard specification of steel plate, i.e. thickness, is shown in the table below. The test hole shall be punched or drilled, and the tolerance is the specified nominal diameter (see the table below) ± 0.025mm.

Specifications	6#	7#	8#	10#	12#	1/4
Thickness of test plate （mm）	1.85-1.95			3.12-3.23		4.68-4.84
Aperture（mm） ±0.025	2.95	3.26	3.45	4.04	4.76	5.50

2、 Wallboard nails:
1. Core hardness: Standard: hrc24-45, the actual measurement of our products is about hrc35-38.
2. Surface hardness: Standard: hv600-800, the actual measurement of our products is about hv660-710.
3. Carburized layer: 4 × 10-6 × 0.05-0.18mm, 8 × 10-12 × 0.10-0.23, 14 × 0.13-0.28
4. Bending: 150 – 450 required
5. Salt spray test: Min 48h in general.
6. Torque:

Specifications	6#	7#	8#	10#
Torsion	21	28	35	58
Measured by our company	35	42	56	96

7. Attack test: see Chapter 1 for details.
3、 Drill tail screw:
1. Core hardness: Standard: hrc32-40, the actual measurement of our products is hrc31.7-39.0.
2. Surface hardness: Standard: hv600-700, the actual measurement of our products is about hv620.
3. Cemented layer:

• 4#-6# ：0.05-0.18mm
• 8#-12#：0.10-0.23mm
• 14#：0.15-0.28mm

4. Torque:

Specifications	Drill tail screw
	TYPE  BSD		TYPE  CSD
	INCH-LB	KG-CM	INCH-LB	KG-CM
4#（2.9）	14	16	14	16
6#（3.5）	24	28	24	28
8#（4.2）	42	48	48	55
10#（4.8）	61	70	65	75
12#（5.5）	92	106	100	115
14#（6.3）	150	173	156	180

5. Attack speed is described in Chapter 1.

Chapter 4. surface defects

1、 The bad phenomenon and reason analysis of the leading.

• 1. Eccentricity: poor installation of the second punch and improper adjustment.
• 2. Tilt head: improper installation and adjustment.
• 3. The head is not round: the selection of a punching die is improper or the forming of one punch is not full enough.
• 4. Punching crack: die cracking or improper R-angle, which causes the die to be scratched by two impacts.
• 5. Head double layer: one punch molding is poor.
• 6. Burr: a poor stamping, mainly due to the gap between the punch and the die hole is too large or the punch bar is too short.
• 7. Crack angle: the needle is broken or the second punch is not heavy with the punch.
• 8. Head cracking: material problems, or the use of a die error (such as a pan head with hexagonal Huasi head die), and the cause of lubricating oil.

2、 Analysis of the causes of tooth rolling

• 1. Processing crack: worn tooth plate and improper adjustment.
• 2. Blunt tail: improper adjustment, too old tooth plate.
• 3. Burning: the distance between the two dental plates is too large, or the feeding time is not correct.
• 4. Skewed tail: the control screw on the die holder is too tight.
• 5. Broken tail: tooth plate wear and improper adjustment.
• 6. Insufficient tooth mountain: improper adjustment
• 7. The tail teeth were not rubbed to the tip of the tail.
• 8. Crooked rod: the correction block is not well corrected.
• 9. The tooth base is rough: the tooth space is not adjusted well.

Part IV technological process

Chapter 1. annealing

1、 Objective: to adjust the crystal structure, reduce the hardness and improve the processability at room temperature by heating the wire to a proper temperature, holding a certain time, and then cooling slowly.
2、 Operation process:
（1） Feeding: lift the products to be treated in the furnace, and pay attention to the furnace cover. Generally, one furnace can process 7 rolls (about 1.2 tons / roll) at the same time.
（2） Heating: slowly raise the temperature in the furnace (about 3-4 hours) to the specified temperature.
（3） Heat preservation: 1018 and 1022 wires are kept at 680 ℃ – 715 ℃ for 4-6h, 10b211039 is used, and ch38f wire is kept for 5.5-7.5h at 740 ℃ – 760 ℃.
（4） Cooling: slow down the temperature in the furnace (about 3-4 hours) to below 550 ℃, and then cool down to normal temperature with the furnace.
3、 Quality control:
1. Hardness: the hardness of 1018 and 1022 wire after annealing is hv120-170, and that of medium carbon wire is hv120-180 after annealing.
2. Appearance: no oxide film and decarburization on the surface.

Chapter 2. pickling

1、 Objective: to remove the oxide film on the surface of wire rod and form a layer of phosphate film on the metal surface, so as to reduce the scratch of tools and dies during wire drawing, cold block or forming.
2、 Operation process:
（1） Acid pickling: immerse the whole pan into three hydrochloric acid tanks with 20-25% concentration at room temperature for several minutes to remove the oxide film on the surface of wire rod.
（2） Clean water: remove the hydrochloric acid corrosion products on the wire surface.
（3） Oxalic acid: increase the activity of metal to make the skin film formed in the next process more compact.
（4） Coating treatment: the pan element is immersed in phosphate, and the steel surface contacts with the formation treatment solution, and the steel dissolves to form insoluble compounds (such as zn2fe (PO4) 2 · 4H2O) and adheres to the steel surface to form a skin film.
（5） Clean water: remove the residue on the surface of skin film.
（6） Lubricant: because the friction coefficient of phosphate film is not very low, it can not give sufficient lubricity during processing, but react with metal soap (such as sodium soap) to form a hard metal soap layer, which can improve its lubricating performance.

Part V standards and specifications

Standards are norms, and each country and department has its own standards. At present, the most commonly used standards in our daily business are as follows:

• GB-china national standard (GB)
• ANSI – American national standard (American Standard)
• DIN – German national standard (German standard)
• ASME – American Society of Mechanical Engineers
• JIS (Japanese standard)
• BSW – British national standard

GB-national standard is one of many standards in China, and there are also industry standards, professional standards and department standards. National standards are divided into: GB (mandatory standards), GB / T (recommended standards) and GBN (national internal standards). What we usually see, such as GB30, GB5783 and so on, are mandatory standards.
In addition to some basic dimensions, such as head to side, head thickness, etc., the main difference of the above standards is the difference of thread part. GB, DIN, JIS and other threads are in mm (mm) units, collectively referred to as metric threads. Another thread such as ANSI, ASME, etc. is in inches, called American Standard thread. In addition to metric thread and American screw thread, there is a bsw-british standard. The thread is also in inch, commonly known as Wyeth thread.
Metric thread is in mm (mm) units, its cusp angle is 60 degrees. Both American and British threads are in inches. The cusp angle of American thread is also 60 degrees, while that of British thread is 55 degrees. Due to the different measurement units, the representation of various threads is not the same. For example, m16-2×60 represents metric thread. His specific meaning is that the nominal diameter of the screw is 16mm, the pitch is 2mm, and the length is 60mm. For example, 1 / 4-20×3 / 4 indicates the British thread. His specific meaning is that the nominal diameter of the screw is 1 / 4 inch (one inch = 25.4mm), and there are 20 teeth on one inch, and the length is 3 / 4 inch. In addition, if you want to indicate American screw, you will usually add uncand UNF after the English screw to distinguish between American coarse tooth and American fine tooth.
In the usual domestic sales business, the standards we often encounter are GB (national standard) and DIN (German standard).
In terms of non fanwo products, we will mainly contact the following standards: GB30; gb5783; gb5782; gb52; GB6170; GB818; GB819; GB845; GB846; GB70; DIN912; DIN933; DIN931, etc. At present, GB30 (old national standard) has been replaced by GB5783 (new national standard) in the standard book. Gb52 (old national standard) has been replaced by GB6170 (new national standard) in the standard book.
In 1986, our country formulated a new standard for standard parts, commonly known as the new standard in business. The most commonly used standards are GB5780, GB5781, GB5782, GB5783 and GB5784. GB5780 is a kind of hexagon head thick rod half thread screw, and its precision grade is grade C, which can be replaced by GB5782 (GB5782 is hexagon head thick rod full thread screw, and its accuracy grade is a and b) GB5781 is a hexagon head full tooth screw, and the accuracy grade is grade C. GB5783 can be replaced by GB5783 (GB5783 is hexagon head full tooth screw, and its accuracy grade is a and b). GB5784 is a hexagon screw with thin rod and half tooth.
The difference between the new standard and the old one is that the width of the opposite side of the products of the series of M8, M10, M12, M14 and M22 is different. In addition to the new products of M22 series, the head opposite sides of new standard products M8, M10, M12 and M14 are 1 mm smaller than those of the old standard. They are 13 mm, 16 mm, 18 mm and 21 mm respectively. For the new products of M22 series, the new standard is 2 mm larger than the opposite side of the old standard, which should be paid special attention to. For the thickness of the head, there is a slight difference between the new standard and the old one, which can be used when the requirements are not very strict.
The difference between the new standard and the German standard is that the product specifications of M14, M22, M14 and M12 are different in width. The head to side new mark of M12, M14 is 1 mm smaller than that of German standard. The M22 new products, its head to side width than the German standard to the side width to be 2mm, other can be used.
For hexagon nuts, the commonly used standards are: GB52, GB6170, GB6172 and DIN934. The main difference between them is that the thickness of GB6170 is thicker than that of GB52, GB6172 and DIN934, commonly known as thick nuts. In addition, the opposite sides of DIN934, GB6170 and GB6172 in the series of M8 nuts are 13mm, which is 1mm smaller than 14mm of GB52. For M12 nut, the opposite side of DIN934 and GB52 is 17mm, which is 1mm larger than that of GB6170 and gb6172. For M12 nut, the opposite side of DIN934 and GB52 is 19mm, which is 1mm larger than that of GB6170 and GB6172. For the nut of GB6172 and GB6172, it is larger than that of GB6172. Another is the M22 nut. The opposite side of DIN934 and GB52 is 32mm, which is 2mm smaller than 34mm of GB6170 and GB6172. (GB6170 and GB6172 have the same width on the opposite side except the thickness is different). Other specifications can be used without considering the thickness.
In terms of internal hexagon, there are two versions in the national standard, one is gb70-76, the other is GB70-85 In 1985, our company implements DIN912 standard, so we should pay attention to the differences in actual business operation: GB70-85 and DIN912 are completely identical, so there is no difference in the use of the new standard, mainly between GB70-76 and DIN912: for the internal hexagon products of M8 series, the round head diameter of GB70-76 is 12.5mm, which is smaller than 13.27mm of DIN912, For M16 series hexagon socket products, the round head diameter of GB70-76 is 15mm, which is smaller than 16.27 of DIN912; for M12 series, the round head diameter of GB70-76 is 18mm, which is smaller than that of DIN912 18.27; for M16 and M20 series, the round head diameter of GB70-76 is 0.33mm smaller than that of DIN912, 24mm and 30mm respectively. 33 mm and 30.33 mm, respectively. In addition, the width of the inner opposite side between the old standard and the German standard is different due to different standards. The inner opposite edge of GB70-76 is smaller, which should be paid attention to in the business operation.
In addition, there are some differences in the carriage screws that may be used at ordinary times. Here is an explanation. In the national standard, there are two kinds of carriage screw standards, namely, GB12 (small half round head square neck screw) and GB14 (large half round head square neck screw), and the German standard DIN603 is more commonly used in the market. The difference between the three is as follows: for the round neck, when compared with the same specification, it is: GB12 < GB14 < DIN603. Usually, when the carriage screw is used, the head and neck are required to be large and thick, so the standard of DIN603 carriage screw fully meets the requirements.

Source: China Fasteners Supplier: www.epowermetals.com

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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