Whereas in the past it was necessary to have screwdrivers in all sizes, today a screwdriver with replaceable head or a cordless screwdriver is used, into which the right bit is used as needed.

Which is the right one, depends on the screw head. Torx are common today, although cross slot is still common and even slotted screws still occur. These bits are each available in different sizes, this is about the diameter.

A set of standard bits of slot, Phillips and Torx each 3-4 sizes, with the sets are particularly recommended in which the three common sizes are listed, but of the most used in each case two pieces. This usually affects the average size. In the case of Torx, for example, this is the number 20 or 25. The size is imprinted on the bits, for example "T25".