Countersink chart
A flush screw only sits flush if the cone in the material matches the cone under the head. Metric flat heads are 90 degrees.
| Size | Head dia | Countersink dia | Depth | Clearance hole |
|---|---|---|---|---|
| M1.2 | 2.3 mm | 2.5 mm | 0.55 mm | 1.4 mm |
| M1.4 | 2.6 mm | 2.8 mm | 0.60 mm | 1.6 mm |
| M1.6 | 3.0 mm | 3.2 mm | 0.70 mm | 1.8 mm |
| M2 | 3.8 mm | 4.0 mm | 0.80 mm | 2.4 mm |
| M2.5 | 4.7 mm | 4.9 mm | 1.00 mm | 2.9 mm |
| M3 | 6.0 mm | 6.2 mm | 1.40 mm | 3.4 mm |
| M4 | 8.0 mm | 8.2 mm | 1.85 mm | 4.5 mm |
| M5 | 10.0 mm | 10.2 mm | 2.35 mm | 5.5 mm |
| M6 | 12.0 mm | 12.2 mm | 2.80 mm | 6.6 mm |
Based on DIN 965 / ISO 7046 head diameters, cut at 90 degrees included angle.
The 82 vs 90 degree trap
US flat head screws are usually 82 degrees. Put one in a 90 degree countersink and it only touches at the bottom edge; put a metric head in an 82 degree hole and it stands proud. If a flush screw will not sit down, check the angle before you blame the depth.
Screw head shapes explained →Gear for this job
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Countersink bit set
Cuts the cone so flat heads sit flush
Countersunk screw assortment
Flush-fitting screws in several sizes