Why do screws have so many joints?

Why do screws have so many joints?

First of all, because the contact area between the slotted and cross openings and the tool is not the same level as the contact area between the inner and outer hexagon and the tool, there is almost no problem of twisting the inner and outer hexagon (but there are also cases where the inner hexagon is screwed into a round hole).

In addition, the screw tightening tools must be appropriate and appropriate (if you want to install them again, they will not be discussed at one time). We will find an inappropriate tool to screw the slotted and cross screws at will (take a strong large screwdriver to screw the small screws on the back of the pen and notebook computer), but it is difficult to find an inappropriate tool in the inner and outer hexagon.
Then, the word and cross screws are not for you to screw hard. It’s OK to screw them with the right force. It’s a pity that the person who wants to screw them down later doesn’t have your strong and skilled skills, so there is a great risk of screwing them.
Finally, the groove is going to spend or has spent. Please replace it with a new one after unscrewing… At the same time, if it is rusty, please solve the problem of rust first and screw it again in addition to rust.
Emphasize that to be a moral person, don’t put the spent screws back! I wish I could find the one who touched it when I met the ugly screw that had been spent.
Don’t look at those engaged in machinery. “If you want to learn machinery well, bolts must be painted skillfully”. How many mechanical students fold the first one on the painted bolt… After folding the painted bolt, fold it on the check bolt. The basic skills of drawing must be solid, so that people can make complaints about others’ drawings later. One can finish drawing and do not have a few pictures of a single mistake.

If you are only talking about the “screw” in standard parts, rather than the more extensive “threaded connector” or “threaded fastener”, the common “screw” also has a cross and a word, and an inner hexagon (it is rare in household appliances, but it can be seen in cars and self driving vehicles). Of course, non-standard parts are unrestrained, just to prevent you from easily disassembling them, so they must be different.
Let’s talk about why there are at least three kinds: a word, a cross and an inner hexagon.
In fact, the word is used less and less, and there will be more carpentry, because it has not many advantages over the cross. The processing cost once considered is now indistinguishable. In addition, it is easier to find substitutes without readily available tools. Now these are not big problems. Many places, or almost all occasions, can be replaced by crosses. The advantage of the cross is that it is not easy to twist (the tools should be appropriate, and it is not easy to twist large or small or vice versa). The hexagon wrench is easier to tighten, because the hexagon wrench usually looks like this:

To expand a little, the main question may also want to ask: why do “joints” have circular, cylindrical and conical?

In fact, it is mainly determined by the application occasion. The last two are countersunk screws. They are used where countersunk screws are needed. If you don’t understand, look at the laptop in turn. They are countersunk screws. Why do you think. Then why not use countersunk heads? Because the countersunk head needs to be processed more (in fact, it is not necessary to use a “special” tool to fix the countersunk head and hole at once), it can save money and trouble on unnecessary occasions. In particular, for the cone, due to the self centering characteristics of the cone, it can ensure that the two connected holes are concentric (see the difference between the third figure and the fourth figure, there is a gap between the counterbore of the cylinder and the screw, but there is no gap in the cone).

Screws and bolts

The main difference between screw and bolt is that the screw works alone, and the thread matched with the screw is processed on the workpiece; The bolt and nut work together, and the thread matched with the bolt is machined on the nut. They play similar roles, but they are used in different occasions. Bolts and nuts are standard parts purchased in advance. As long as the connected objects are punched with a suitable through hole, it is simple and low cost; The screw is used where the bolt cannot be used. For example, one of the linked objects is too thick (or for other reasons) to make a hole, so the threaded hole has to be machined on it and connected with the screw, which increases the cost (the threaded hole needs to be tapped more than the smooth hole).
Look at the figure. The following is the schematic diagram of screw and screw connection.

Source:  China Screw supplier: www.epowermetals.com