The screw

 

A screw is a cylindrical or slightly tapered (conical) body in whose surface a thread is cut or rolled. A screw head is attached to one end. The force is transmitted to the workpiece to be fastened via the "chin" of the screw head (ring surface, bottom). A plate through which the screw is inserted is often fastened in this way. The screw head is shaped at the edge or on its upper side in such a way that it can be connected with a tool (a screwdriver or a wrench) for screwing in and out.

 

The two main types of screw differ in the thread.

 

Metal screws

Their shank and the contour of the thread are cylindrical. They are only screwed into parts with suitable counter threads (nut threads). Metal screws are also usually made of metal and less often of relatively solid plastics (the parts into which they are screwed are more often made of plastic).

 

Wood screws

The threaded shaft part is slightly tapered and ends in a sharp point. The flanks of the thread are sharper than those of metal screws. These three form elements are a prerequisite for the wood screw to penetrate into the piece of wood automatically during the screwing process and to cut a thread. To support the screwing process, a smaller diameter is often used for pre-drilling. The same applies to screwing wood screws into plastic parts.

 

Further information on the subject of screws can be found here