Phillips head screwdrivers come in five sizes, numbered from 0 to 4. Phillips head screw sizes are based on numbers as well, ranging from 0 to 24. Because there are only five screwdriver sizes, each one corresponds to two or more screw sizes.
Phillips head screwdrivers come in sizes indicated by numbers rather than actual measurements, as is also the case with flathead screwdrivers. Phillips head screwdriver size #0 fits screw numbers 0 and 1, the Phillips head driver size #1 fits screw numbers 2, 3 and 4. Phillips head screwdriver size #2 fits screw numbers 5, 6, 7, 8 and 9, the most of all sizes. Size #3 Phillips head screwdriver works on screws with the numbers 10, 12, 14 and 16, and the #4 Phillips head fits in screw sizes 18, 20 and 24.
The sizes of the handles on Phillips head screwdrivers vary depending on the set that it came from. Certain sets contain a special stubby Phillips head driver with a shaft measuring approximately 1 inch. There are many Phillips head screwdrivers with slight variations in the handle, shaft and tip, but all Phillips head screwdrivers come in the same standard five sizes. Phillips head screwdrivers only fit in crosshead screws; however, flathead screwdrivers may sometimes fit in crosshead screws as well.