Unsure on what size countersunk hole to use for your ANSI Metric socket flat head fasteners?
Use the image and chart below to determine what dimensions to use, all dimensions are in millimeters apart from the countersink angle.
For example, an ANSI Metric M6 flat head screw with a normal fit countersunk hole will require a pilot hole diameter of 6.6 mm, a countersunk diameter of 13.71 mm, and a countersunk angle of 90°.
Countersunk Hole Size Chart for Socket Flat Head Fasteners (ANSI Metric)
All dimensions are in millimeters apart from the countersink angle.
| Fastener Size (Thread) | Pilot Hole Diameter (Close Fit H12) | Pilot Hole Diameter (Normal Fit H13) | Pilot Hole Diameter (Loose Fit H14) | Countersink Diameter | Countersink Angle (°) |
| M3 | 3.2 | 3.4 | 3.6 | 6.94 | 90 |
| M3.5 | 3.7 | 3.9 | 4.2 | 6.94 | 90 |
| M4 | 4.3 | 4.5 | 4.8 | 9.18 | 90 |
| M5 | 5.3 | 5.5 | 5.8 | 11.47 | 90 |
| M6 | 6.4 | 6.6 | 7 | 13.71 | 90 |
| M8 | 8.4 | 9 | 10 | 18.25 | 90 |
| M10 | 10.5 | 11 | 12 | 22.73 | 90 |
| M12 | 13 | 13.5 | 14.5 | 27.21 | 90 |
| M16 | 17 | 17.5 | 18.5 | 33.99 | 90 |
| M20 | 21 | 22 | 24 | 40.71 | 90 |
| M24 | 25 | 26 | 28 | 41 | 90 |