COUNTERBORE HOLE DIMENSIONS CHART (INCH)

Counterbore hole dimensions chart for inch socket head cap screws.

Counter Bore Hole Dimensions
Nom. Size or Basic Screw Dia.  Normal Drill Size, A H B C
Close Fit Normal Fit
Number or
Fractional
Size		 Decimal
Size		 Number or
Fractional
Size		 Decimal
Size
0  0.0600 51 0.067 49 0.073 0.060 1/8 0.074
1 0.0730 46 0.081 43 0.089 0.073 5/32 0.087
2 0.0860 3/32 0.094 36 0.106 0.086 3/16 0.102
3 0.0990 36 0.106 31 0.120 0.099 7/32 0.115
4 0.1120 1/8 0.125 29 0.136 0.112 7/32 0.130
5 0.1250 9/64 0.141 23 0.154 0.125 1/4 0.145
6 0.1380 23 0.154 18 0.170 0.138 9/32 0.158
8 0.1640 15 0.180 10 0.194 0.164 5/16 0.188
10 0.1900 5 0.206 2 0.221 0.190 3/8 0.218
1/4 0.2500 17/64 0.266 9/32 0.281 0.250 7/16 0.278
Nom. Size or Basic Screw Dia.  Normal Drill Size, A H B C
Close Fit Normal Fit
Number or
Fractional
Size		 Decimal
Size		 Number or
Fractional
Size		 Decimal
Size
5/16 0.3125 21/64 0.328 11/32 0.344 0.312 17/32 0.346
3/8 0.3750 25/64 0.391 13/32 0.406 0.375 5/8 0.415
7/16 0.4375 29/64 0.453 15/32 0.469 0.438 23/32 0.483
1/2 0.5000 33/64 0.516 17/32 0.531 0.500 13/16 0.552
5/8 0.6250 41/64 0.641 21/32 0.656 0.625 1 0.689
3/4 0.7500 49/64 0.766 25/32 0.781 0.750 1 3/16 0.828
7/8 0.8750 57/64 0.891 29/32 0.906 0.875 1 3/8 0.963
1 1.0000 1 1/64 1.016 1 1/32 1.031 1.000 1 5/8 1.100
1 1/4 1.2500 1 9/32 1.281 1 5/16 1.312 1.250 2 1.370
1 1/2 1.5000 1 17/32 1.531 1 9/16 1.562 1.500 2 3/8 1.640
1 3/4 1.7500 1 25/32 1.781 1 13/16 1.812 1.750 2 3/4 1.910
2 2.0000 2 1/32 2.031 2 1/16 2.062 2.000 3 1/8 2.180

Note 1: B - Counterbore Diameter, C - Countersink Diameter, H - Counterbore Depth / Max. Head Height for Socket Head Cap Screw

Note 2: All dimensions are in inches.

Supplements:

Reference:

  • Oberg, E. , Jones ,F.D. , Horton H.L. , Ryffel H.H., (2016) . Machinery's Handbook . 30th edition.  Industrial Press Inc.
  • Oberg, E. , Jones ,F.D. , Horton H.L. , Ryffel H.H., (2012) . Machinery's Handbook . 29th edition.  Industrial Press Inc.