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Countersink & Counterbore Dimensions
Look up standard countersink and counterbore dimensions for metric (ISO 10642 / ISO 4762) and imperial (ASME B18.3 / B18.6.2) fasteners. Includes through-hole sizes, countersink diameters for flat head screws, and counterbore dimensions for socket head cap screws.
Dimension Lookup
M8 — Countersink Dimensions
Through Hole (ISO 273 Normal):9 mm
Countersink ∅ (90°):17.92 mm
Countersink Depth:4.96 mm
Standard:ISO 10642 / DIN 7991 (90°)
Metric Countersink & Counterbore Table (mm)
| Size | Through Hole | CSK ∅ (90°) | CSK Depth | CBore ∅ | CBore Depth | SHCS Head ∅ |
|---|---|---|---|---|---|---|
| M3 | 3.4 | 6.72 | 1.86 | 6.5 | 3.5 | 5.5 |
| M4 | 4.5 | 8.96 | 2.48 | 8 | 4.5 | 7 |
| M5 | 5.5 | 11.2 | 3.1 | 9.5 | 5.5 | 8.5 |
| M6 | 6.6 | 13.44 | 3.72 | 11 | 6.5 | 10 |
| M8 | 9 | 17.92 | 4.96 | 14.5 | 9 | 13 |
| M10 | 11 | 22.4 | 6.2 | 18 | 11 | 16 |
| M12 | 13.5 | 26.88 | 7.44 | 20 | 13 | 18 |
| M14 | 15.5 | 30.8 | 8.4 | 23 | 15 | 21 |
| M16 | 17.5 | 33.6 | 8.8 | 26 | 17 | 24 |
| M18 | 20 | 36 | 9 | 29 | 19 | 27 |
| M20 | 22 | 40.32 | 10.16 | 33 | 21 | 30 |
| M24 | 26 | 48 | 12 | 40 | 25 | 36 |
Imperial Countersink & Counterbore Table (mm)
| Size | Through Hole | CSK ∅ (82°) | CBore ∅ | CBore Depth |
|---|---|---|---|---|
| #4 (0.112") | 3.26 | 5.56 | 6.53 | 3.05 |
| #6 (0.138") | 3.8 | 6.78 | 7.75 | 3.56 |
| #8 (0.164") | 4.5 | 8 | 8.97 | 4.06 |
| #10 (0.190") | 5.11 | 9.27 | 10.19 | 4.57 |
| 1/4" | 6.76 | 12.19 | 12.7 | 6.35 |
| 5/16" | 8.43 | 15.24 | 15.88 | 7.94 |
| 3/8" | 10.31 | 18.29 | 19.05 | 9.53 |
| 7/16" | 11.91 | 21.34 | 22.23 | 11.11 |
| 1/2" | 13.49 | 24.38 | 25.4 | 12.7 |
| 5/8" | 17.07 | 30.48 | 31.75 | 15.88 |
| 3/4" | 20.65 | 36.58 | 38.1 | 19.05 |
| 1" | 27.79 | 48.77 | 50.8 | 25.4 |
Notes & Standards
- Countersink (CSK): Conical recess for flat head screws to sit flush with surface. Metric uses 90° angle (ISO 10642), Imperial uses 82° angle (ASME B18.6.2).
- Counterbore (CBore): Cylindrical flat-bottomed recess for socket head cap screws (SHCS) to sit below surface. Dimensions per ISO 4762 (metric) / ASME B18.3 (imperial).
- Through hole: Clearance hole for the bolt shank, normal fit per ISO 273.
- Depth: Counterbore depth ensures the screw head is fully recessed. Add 0.5–1mm clearance for practical applications.
Reference: ISO 10642 (Countersunk socket head cap screws), ISO 4762 (Socket head cap screws), ISO 273 (Clearance holes), ASME B18.3, ASME B18.6.2.