A screw is a pin or bolt with an external thread. A connection made with a screw is usually non-positive and positive and can be released again. A basic distinction is made between so-called wood and metal screws. Wood screws are slightly conical and are mainly screwed into wood in which they cut a counter thread themselves. A special and adapted counterpart like the nut does not exist. A metal screw is usually cylindrical and is screwed into a counter thread which is located in the nut or another part involved in the connection. It is called a metal screw because it was developed in the metal industry and is mainly used there.