Choosing the right screw for the job can be quite complicated as there are variations in materials, plated finishes, head styles, sizes and thread types. In addition to different head styles there are two basic head slot styles - the traditional slotted-head style and the so-called cross-head style. Unfortunately, there are three cross-head styles which can be difficult to identify. The most familiar one - Pozidriv is found mainly on wood screws. The more recent Supadriv head is similar and is said to give more grip between the screw and screwdriver, though in practice with wood screws the difference is not significant. The third style, known as Phillips, is found mainly on machine and self-tapping screws fitted to products manufactured on the Continent and in the Far East. Traditional slotted-head screws are turned by means of a single slot into which a screwdriver blade should fit snugly. Because the slot size varies with the screw, a range of screwdrivers is needed to cope with all ...