ASME B18.6.3 Type 3 Square Recessed Undercut Flat Countersunk Head Machine Screws

ASME B18.6.3 Type 3 Square Recessed Undercut Flat Countersunk Head Machine Screws

Dimensions of Type 3 Square Recessed Undercut Flat Countersunk Head Machine Screws

Nominal Size or Basic Screw Diameter Length, L Head Diameter, A Head Height, H Recess Across Flats, M Recess Depth, T Recess Size Recess Penetration Gaging Depth Protrusion Above Gaging Diameter, F Gaging Diameter, G
Max Min Max Min Max Min Max Min
4 3/16 0.212 0.191 0.047 0.038 0.050 0.057 00 0.033 0.028 0.032 0.019 0.172
5 3/16 0.237 0.215 0.053 0.043 0.070 0.066 0 0.038 0.028 0.034 0.020 0.196
6 3/16 0.262 0.238 0.059 0.048 0.091 0.070 1SS 0.027 0.017 0.036 0.021 0.220
8 1/4 0.312 0.285 0.070 0.058 0.112 0.091 2SS 0.037 0.027 0.039 0.023 0.267
10 5/16 0.362 0.333 0.081 0.068 0.112 0.091 2SS 0.037 0.027 0.042 0.025 0.313
12 3/8 0.412 0.380 0.092 0.078 0.133 0.138 3SS 0.073 0.063 0.045 0.027 0.362
1/4 7/16 0.477 0.442 0.107 0.092 0.133 0.143 3S 0.080 0.065 0.050 0.029 0.424
5/16 1/2 0.597 0.556 0.134 0.116 0.191 0.194 4R 0.100 0.085 0.057 0.034 0.539
3/8 9/16 0.717 0.670 0.161 0.140 0.191 0.194 4R 0.100 0.085 0.065 0.039 0.653

Note :

  • Where specifying nominal size in decimals, zeros preceding the decimals and in the fourth decimal place shall be omitted.
  • Screws of these length and shorter shall have undercut heads.
  • Tabulated values determined from formula for maximum H in Appendix A.
  • "R" in the recess size tabulation means regular depth recess, the "S" mean short depth recess, and the "SS" means "short-short" depth recess.
  • Square recesses incorporate a slight taper on the sides of the recess. This taper can result in loss of penetration gaging depth on finished fasteners due to the build up of plating in the 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.
  • No tolerance for gaging diameter is given. If the gaging diameter of the gage used differs from tabulated value, the protrusion will be affected accordingly and the proper protusion values must be recalculated using the formulas.