Countersink & Counterbore Chart
Counterbore and countersink dimensions for socket-head cap screws, flat-head cap screws, button-head, and metric equivalents. Hole diameter, depth, and included-angle values for inch (ANSI) and metric (ISO/DIN) fasteners.
Reference
Counterbore = cylindrical pocket for socket-head / button-head screws to sit flush. Countersink = conical pocket for flat-head screws (82° for standard UNC / UNF cap screws, 90° for metric ISO 10642 / DIN 7991, 100° for aerospace / 110° for some flat-head sheet-metal screws). Data reflects screw head nominal + typical clearance recommendation for class 1 fit.
Socket-head cap screw (ASME B18.3) — inch
| Screw | Head Ø (max) | Head Height | Counterbore Ø | Counterbore Depth |
|---|---|---|---|---|
| #0 (0.060) | 0.096 | 0.060 | 7/64 (0.109) | 0.060 |
| #2 (0.086) | 0.140 | 0.086 | 5/32 (0.156) | 0.086 |
| #4 (0.112) | 0.183 | 0.112 | 7/32 (0.219) | 0.112 |
| #6 (0.138) | 0.226 | 0.138 | 1/4 (0.250) | 0.138 |
| #8 (0.164) | 0.270 | 0.164 | 9/32 (0.281) | 0.164 |
| #10 (0.190) | 0.312 | 0.190 | 5/16 (0.312) | 0.190 |
| 1/4 | 0.375 | 0.250 | 13/32 (0.406) | 0.250 |
| 5/16 | 0.469 | 0.312 | 1/2 (0.500) | 0.312 |
| 3/8 | 0.563 | 0.375 | 19/32 (0.594) | 0.375 |
| 7/16 | 0.656 | 0.438 | 11/16 (0.688) | 0.438 |
| 1/2 | 0.750 | 0.500 | 25/32 (0.781) | 0.500 |
| 5/8 | 0.938 | 0.625 | 31/32 (0.969) | 0.625 |
| 3/4 | 1.125 | 0.750 | 1-5/32 (1.156) | 0.750 |
| 7/8 | 1.313 | 0.875 | 1-11/32 (1.344) | 0.875 |
| 1" | 1.500 | 1.000 | 1-1/2 (1.500) | 1.000 |
Socket-head cap screw (DIN 912 / ISO 4762) — metric
| Screw | Head Ø | Head Height | Counterbore Ø | Counterbore Depth |
|---|---|---|---|---|
| M2 | 3.8 mm | 2.0 mm | 4.3 mm | 2.4 mm |
| M2.5 | 4.5 mm | 2.5 mm | 5.0 mm | 2.9 mm |
| M3 | 5.5 mm | 3.0 mm | 6.5 mm | 3.4 mm |
| M4 | 7.0 mm | 4.0 mm | 8.0 mm | 4.6 mm |
| M5 | 8.5 mm | 5.0 mm | 10.0 mm | 5.7 mm |
| M6 | 10.0 mm | 6.0 mm | 11.0 mm | 6.8 mm |
| M8 | 13.0 mm | 8.0 mm | 15.0 mm | 9.0 mm |
| M10 | 16.0 mm | 10.0 mm | 18.0 mm | 11.0 mm |
| M12 | 18.0 mm | 12.0 mm | 20.0 mm | 13.0 mm |
| M14 | 21.0 mm | 14.0 mm | 24.0 mm | 15.0 mm |
| M16 | 24.0 mm | 16.0 mm | 26.0 mm | 17.5 mm |
| M20 | 30.0 mm | 20.0 mm | 33.0 mm | 21.5 mm |
| M24 | 36.0 mm | 24.0 mm | 40.0 mm | 25.5 mm |
Flat-head cap screw (82° countersink, ASME B18.3.2)
| Screw | Head Ø (max) | Countersink Ø | Countersink Depth |
|---|---|---|---|
| #4 | 0.225 | 0.240 | 0.081 |
| #6 | 0.279 | 0.300 | 0.108 |
| #8 | 0.332 | 0.360 | 0.130 |
| #10 | 0.385 | 0.420 | 0.153 |
| 1/4 | 0.507 | 0.535 | 0.199 |
| 5/16 | 0.635 | 0.668 | 0.249 |
| 3/8 | 0.762 | 0.795 | 0.298 |
| 7/16 | 0.812 | 0.845 | 0.319 |
| 1/2 | 1.017 | 1.054 | 0.399 |
| 5/8 | 1.270 | 1.314 | 0.499 |
| 3/4 | 1.525 | 1.573 | 0.599 |
| 1" | 2.030 | 2.090 | 0.800 |
Flat-head cap screw (90° countersink, DIN 7991 / ISO 10642) — metric
| Screw | Head Ø | Countersink Ø | Countersink Depth |
|---|---|---|---|
| M2 | 3.8 mm | 4.0 mm | 1.2 mm |
| M2.5 | 4.7 mm | 5.0 mm | 1.5 mm |
| M3 | 6.0 mm | 6.5 mm | 1.7 mm |
| M4 | 8.0 mm | 8.5 mm | 2.3 mm |
| M5 | 10.0 mm | 10.5 mm | 2.8 mm |
| M6 | 12.0 mm | 12.5 mm | 3.3 mm |
| M8 | 16.0 mm | 16.5 mm | 4.4 mm |
| M10 | 20.0 mm | 20.5 mm | 5.5 mm |
| M12 | 24.0 mm | 24.5 mm | 6.5 mm |
| M16 | 30.0 mm | 30.5 mm | 7.5 mm |
| M20 | 36.0 mm | 36.5 mm | 8.5 mm |
Button-head cap screw (ANSI B18.3.4) — inch
| Screw | Head Ø | Head Height | Counterbore Ø |
|---|---|---|---|
| #0 | 0.114 | 0.033 | 0.130 |
| #4 | 0.213 | 0.061 | 0.225 |
| #6 | 0.262 | 0.075 | 0.275 |
| #8 | 0.312 | 0.089 | 0.328 |
| #10 | 0.361 | 0.103 | 0.375 |
| 1/4 | 0.437 | 0.140 | 0.453 |
| 5/16 | 0.547 | 0.176 | 0.562 |
| 3/8 | 0.656 | 0.211 | 0.672 |
| 1/2 | 0.875 | 0.281 | 0.891 |
Countersink angle reference
- 82°
- Standard UNC / UNF flat-head cap screws (ASME B18.3.2). Most common in North America.
- 90°
- Metric flat-head screws (DIN 7991, ISO 10642). Also used for some oversize imperial flat-heads.
- 100°
- Aerospace flat-head (MS14218, NAS1351). Lower profile, better for high-strength thin-wall panels.
- 120°
- Sheet-metal / wood screws.
- 60°
- Centre-drill spotting; not for fastener countersinking.
Tips
- For counterbores, drill the clearance hole first, then counterbore — the pilot on the counterbore tool rides in the hole.
- Depth rule: counterbore depth = head height + 0.005 to 0.030" (thin panels use the low end so the screw grips through).
- For structural joints, recess the head at least 0.010" below the surface to protect the head and improve gasket seating.
- Countersink tools have a leading angle rating (e.g. 82° × 1/2"). Match the angle to the screw standard — using an 82° sink on a 90° metric screw (or vice versa) leaves line contact instead of full seat and the screw will never tighten correctly.
- For production, combination drill-and-countersink tools ("screwmachine" style) do both operations in one pass.
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