As a guide, our Square Drive screws use the following driver bit sizes, except as noted within the price list. (In special cases a non-standard recess is used. For instance, #7 and #8 trim head screws normally have a #1 recess in order to avoid breakage problems with the undersized head).

Finally, there are really only two sizes of driver bits in common usage: #1 and #2 Square. They will fit 90% of the screws you are likely to use – screw sizes #6, 8 and 10. Other bits fit screws designed for rather specialized applications. In fact, the #4 driver bit is such a rare beast that it is virtually manufactured to order. We don’t carry screws to fit the bit, but we do carry the bit!

Bit Tip Dimensions
Bit Size	Max	Min	Fraction
#0	0.071	.0696	1/16+
#1	0.091	.090	3/32-
#2	0.1126	.111	7/64+
#3	0.133	0.1315	1/8+
#4	0.191	0.1895	3/16+