What are screws used for?

mainly for woodworking to seal things in place, but they can be used with metals too. The most common screws are the slotted-head screw, round-head screw, and flat-head screw. More recent varieties include the Phillips-head and the Robertson-head screws. All of these vary in length from 6 to 100 mm. they are graded in size from 0 to 24 gauge. Most are made of mild steel but they are also manufactured out of brass and copper for use where moisture is a problem, such as in boat building.