ASME B18.6.3 Type 3 Square Recessed Binding Head Machine Screws

Nominal Size or Basic Screw Diameter	Head Diameter, A		Head Height, O		Head Oval Height, F	Recess Across Flats, M	Recess Depth, T	Recess Size	Recess Penetration Gaging Depth, P
Nominal Size or Basic Screw Diameter	Max	Min	Max	Min	Head Oval Height, F	Recess Across Flats, M	Recess Depth, T	Recess Size	Max	Min
3	0.208	0.197	0.059	0.052	0.020	0.070	0.070	0	0.038	0.023
4	0.235	0.223	0.068	0.061	0.022	0.070	0.070	0	0.038	0.023
5	0.263	0.249	0.078	0.069	0.025	0.091	0.100	1S	0.055	0.040
6	0.290	0.275	0.087	0.078	0.028	0.091	0.100	1S	0.055	0.040
8	0.344	0.326	0.105	0.095	0.034	0.112	0.120	2S	0.063	0.048
10	0.399	0.378	0.123	0.112	0.040	0.112	0.120	2S	0.063	0.048
12	0.454	0.430	0.141	0.130	0.045	0.133	0.178	3S	0.080	0.065
1/4	0.525	0.498	0.165	0.152	0.044	0.133	0.178	3S	0.080	0.065
5/16	0.656	0.622	0.209	0.194	0.068	0.191	0.199	4R	0.100	0.080
3/8	0.788	0.746	0.253	0.235	0.083	0.191	0.199	4R	0.100	0.080

Note :

Break sharp edge on head where spherical and conical surfaces meet.
Where specifying nominal size in decimals, zeros preceding the decimals and in the fourth decimal place shall be omitted.
"R" in the recess size tabulation means regular depth recess and the "S" means short depth recess.
Square recesses incorporate a slight taper on the sides od the recess. This taper can result in loss of penetration gaging depth on finished fasteners due to the build up of plating in recesses. The recess penetrations dimensions specified here are for finished (plated) product. Manufactures should be advised that they should not use all this tolerance in the heading process, or an out of tolerance condition could exist after plating.