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

Nominal Size or Basic Screw Diameter	Head Diameter, A		Head Height, H		Head Radius, R, Min	Recess Across Flats, M	Recess Depth, T	Recess Size	Penetration Gaging Depth, P
Nominal Size or Basic Screw Diameter	Max	Min	Max	Min	Head Radius, R, Min	Recess Across Flats, M	Recess Depth, T	Recess Size	Max	Min
3	0.193	0.180	0.078	0.069	0.010	0.070	0.066	0	0.038	0.028
4	0.219	0.205	0.086	0.076	0.010	0.070	0.066	0	0.038	0.028
5	0.245	0.231	0.095	0.085	0.015	0.091	0.106	1R	0.065	0.050
6	0.270	0.256	0.103	0.093	0.015	0.091	0.106	1R	0.065	0.050
8	0.322	0.306	0.120	0.110	0.015	0.112	0.127	2R	0.075	0.060
10	0.373	0.357	0.137	0.126	0.020	0.112	0.127	2R	0.075	0.060
12	0.425	0.407	0.153	0.141	0.025	0.133	0.158	3R	0.095	0.080
1/4	0.492	0.473	0.175	0.162	0.035	0.133	0.158	3R	0.095	0.080
5/16	0.615	0.594	0.218	0.203	0.040	0.191	0.194	4R	0.100	0.085
3/8	0.740	0.716	0.261	0.244	0.040	0.191	0.194	4R	0.100	0.085

Note :

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
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.