Metric tap drill chart
For ISO metric threads the tap drill is the diameter minus the pitch, rounded to a drill you can buy: M8 x 1.25 takes 8 − 1.25 = 6.75, so a 6.8 mm drill. Plain "M8" always means the coarse pitch. The inch column helps when only number or letter drills are at hand; the thread column shows the percentage of a full thread the drill leaves.
| Thread | Tap drill | Inch | % | Inch drill | Clear. |
|---|---|---|---|---|---|
| M1.6 x 0.35 | 1.25 mm | 0.0492 | 77% | – | 1.8 mm |
| M2 x 0.4 | 1.6 mm | 0.0630 | 77% | #52 75% | 2.4 mm |
| M2.5 x 0.45 | 2.05 mm | 0.0807 | 77% | #46 76% | 2.9 mm |
| M3 x 0.5 | 2.5 mm | 0.0984 | 77% | #39 73% | 3.4 mm |
| M3.5 x 0.6 | 2.9 mm | 0.1142 | 77% | #32 71% | – |
| M4 x 0.7 | 3.3 mm | 0.1299 | 77% | – | 4.5 mm |
| M5 x 0.8 | 4.2 mm | 0.1654 | 77% | #19 75% | 5.5 mm |
| M6 x 1 | 5 mm | 0.1969 | 77% | #8 73% | 6.6 mm |
| M8 x 1.25 | 6.8 mm | 0.2677 | 74% | H 77% | 9 mm |
| M10 x 1.5 | 8.5 mm | 0.3347 | 77% | R 71% | 11 mm |
| M12 x 1.75 | 10.2 mm | 0.4016 | 79% | Y 77% | 13.5 mm |
| M14 x 2 | 12 mm | 0.4724 | 77% | – | 15.5 mm |
| M16 x 2 | 14 mm | 0.5512 | 77% | – | 17.5 mm |
| M18 x 2.5 | 15.5 mm | 0.6102 | 77% | – | – |
| M20 x 2.5 | 17.5 mm | 0.6890 | 77% | – | 22 mm |
| M22 x 2.5 | 19.5 mm | 0.7677 | 77% | – | – |
| M24 x 3 | 21 mm | 0.8268 | 77% | – | 26 mm |
| Thread | Tap drill | Inch | % | Inch drill | Clear. |
|---|---|---|---|---|---|
| M6 x 0.75 | 5.2 mm | 0.2047 | 82% | #4 71% | 6.6 mm |
| M8 x 1 | 7 mm | 0.2756 | 77% | J 74% | 9 mm |
| M10 x 1.25 | 8.8 mm | 0.3465 | 74% | S 72% | 11 mm |
| M10 x 1 | 9 mm | 0.3543 | 77% | T 70% | 11 mm |
| M12 x 1.5 | 10.5 mm | 0.4134 | 77% | Z 78% | 13.5 mm |
| M12 x 1.25 | 10.8 mm | 0.4252 | 74% | – | 13.5 mm |
| M14 x 1.5 | 12.5 mm | 0.4921 | 77% | – | 15.5 mm |
| M16 x 1.5 | 14.5 mm | 0.5709 | 77% | – | 17.5 mm |
| M18 x 1.5 | 16.5 mm | 0.6496 | 77% | – | – |
| M20 x 1.5 | 18.5 mm | 0.7284 | 77% | – | 22 mm |
| M22 x 1.5 | 20.5 mm | 0.8071 | 77% | – | – |
| M24 x 2 | 22 mm | 0.8661 | 77% | – | 26 mm |
Clearance is the ISO 273 medium (normal) fit. "Inch drill" is the number or letter drill closest to 75% thread that stays inside the 6H minor diameter, where one exists. Method and sources on How we calculate.