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Woodscrews are described in accordance to
the shape of their head, the type of screwdriver that is used to put them in, their
thickness, what they are made from and their length.
Usually the three main shapes for heads are countersunk head, raised head and round head.
The two main types of screwdriver used are crosspoint and flat which fit screws with a
crossed slot in their head or a straight slot. Thickness is determined by the job that is
to be done and the strength required. A No. 4 screw for example is very thin whilst a No.
14 screw is very thick. The most common in use are No. 6 and No. 8.
The length of the screw is determined by how thick the material is that is being fixed.
Before a screw is driven into wood preparation is required. First a
pilot hole is drilled the full length of the screw (this is a small hole to prevent
splitting when the screw is put in), then a larger hole is drilled to allow for the shank
of the screw (the shank is the bit just under the head which does not have threads on it),
then if the screw is countersunk the top of the hole is shaped to take the shape of the
underside of the head. The material from which a screw is made depends on its job. For
example a stainless steel screw could well be used for inside a shower, a steel screw for
inside work and a brass screw for fixing a toilet to the floor.
Some screws are specialised, they may have a double thread to enable them to be driven in
twice as quickly or they may have a very open thread for such materials as chipboard.
The diagrams below indicate the main head shapes and the method of preparation before
inserting a screw.
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