Screws are a common fixing and come in a wide a variety of styles and sizes. Some screws will be for general use while others are designed for a specific purpose. Always use the most appropriate screw for the job and select the correct screwdriver. This not only makes the job easier it will prevent damage to the screw head.
Generally, three factors govern the description of screws: the length, the gauge and the type of head.The length of a screw refers to how much of it is embedded into the material. Therefore the length of a countersink screw is measured from its point to the top of the head, while a round head screw is measured from the point to the top of the shank.
A screw's gauge refers to the diameter of the shank with most screws being available in gauges from 2 (2mm or 1/8 in) to 14 (6.5mm or 9/16 in), and as we can see, the smaller the gauge, the narrower the screw.
Instantly recognisable by the single slot across the diameter of the screw head.
The head of a pan head screw will sit slightly above the surrounding surface and resembles a flattened round head.