For a Socket Head Cap Screw (SHCS) to sit flush, the counterbore must be slightly larger and deeper than the actual bolt head. This chart combines Actual Head Size with Recommended Counterbore Specs.
| Bolt Size | Head Size (Dia/Ht) | C'bore Dia (Rec/Range) | Depth (Rec/Range) |
|---|---|---|---|
| #4 (0.112") | 183 thou Dia112 thou Ht |
218 thou Rec205-230 thou |
125 thou Rec115-140 thou |
| #6 (0.138") | 226 thou Dia138 thou Ht |
265 thou Rec250-280 thou |
155 thou Rec140-170 thou |
| #8 (0.164") | 270 thou Dia164 thou Ht |
312 thou Rec295-330 thou |
185 thou Rec170-200 thou |
| #10 (0.190") | 312 thou Dia190 thou Ht |
360 thou Rec340-380 thou |
215 thou Rec200-230 thou |
| 1/4" (0.250") | 375 thou Dia250 thou Ht |
437 thou Rec410-460 thou |
280 thou Rec260-310 thou |
| 3/8" (0.375") | 562 thou Dia375 thou Ht |
656 thou Rec625-685 thou |
415 thou Rec390-440 thou |
| M3 | 4.5 mm Dia2.0 mm Ht |
6.0 mm Rec5.5-6.5 mm |
3.0 mm Rec2.5-3.5 mm |
| M4 | 5.5 mm Dia2.8 mm Ht |
7.5 mm Rec7.0-8.5 mm |
4.0 mm Rec3.5-4.5 mm |
| M5 | 7.0 mm Dia3.5 mm Ht |
9.5 mm Rec9.0-10.5 mm |
5.0 mm Rec4.5-5.5 mm |
| M6 | 8.5 mm Dia4.0 mm Ht |
11.0 mm Rec10.5-12.0 mm |
6.0 mm Rec5.5-7.0 mm |
| M8 | 10.0 mm Dia5.0 mm Ht |
15.0 mm Rec14.0-16.5 mm |
8.0 mm Rec7.5-9.5 mm |
| M10 | 13.0 mm Dia6.0 mm Ht |
18.0 mm Rec17.0-19.5 mm |
10.0 mm Rec9.5-11.5 mm |
| M12 | 16.0 mm Dia7.0 mm Ht |
21.0 mm Rec20.0-23.0 mm |
12.0 mm Rec11.5-13.5 mm |