How to calculate tap drill size
For a cutting tap the rule is nominal diameter minus pitch: M8 × 1.25 gives 6.75 mm, rounded to the standard 6.8 mm drill.
Forming tap drill size
A forming tap makes no chips: it displaces the material to form the thread. That is why the hole is larger, roughly halfway between pitch diameter and major diameter: as a rule of thumb, nominal diameter minus half the pitch. For M8 the range is 7.37–7.52 mm. The chart gives an indicative range: from the lowest to the highest value given by OSG (class 6HX), Yamawa (class ISO2X) and Emuge; 6GX and 7GX taps need a few hundredths more. Within the range the right value depends on the tap and the material: always check the tap manufacturer's catalogue.
Coarse and fine pitch
The same nominal size needs different tap drills depending on the pitch: M10 coarse (1.5) needs 8.5 mm, M10 × 1 needs 9 mm. Always read the pitch on the drawing.
Metric tap drill chart, coarse and fine pitch
Forming taps: values are indicative. Always check your own tap supplier's catalogue: each manufacturer gives its own range.
| Thread | Pitch (mm) | Cutting tap (mm) | Forming tap, indicative range (mm) |
|---|---|---|---|
| M1 | 0.25 | 0.75 | 0.87 – 0.92 |
| M1.2 | 0.25 | 0.95 | 1.07 – 1.11 |
| M1.4 | 0.30 | 1.10 | 1.24 – 1.30 |
| M1.6 | 0.35 | 1.25 | 1.43 – 1.48 |
| M1.8 | 0.35 | 1.45 | 1.65 – 1.68 |
| M2 | 0.40 | 1.60 | 1.80 – 1.85 |
| M2.2 | 0.45 | 1.75 | 2.01 – 2.04 |
| M2.5 | 0.45 | 2.05 | 2.27 – 2.34 |
| M3 | 0.50 | 2.50 | 2.76 – 2.83 |
| M3.5 | 0.60 | 2.90 | 3.22 – 3.30 |
| M4 | 0.70 | 3.3 | 3.66 – 3.73 |
| M4 × 0.5 | 0.50 | 3.5 | 3.77 – 3.82 |
| M5 | 0.80 | 4.2 | 4.60 – 4.68 |
| M5 × 0.5 | 0.50 | 4.5 | 4.77 – 4.82 |
| M6 | 1.00 | 5.0 | 5.50 – 5.60 |
| M6 × 0.75 | 0.75 | 5.2 | 5.65 – 5.71 |
| M6 × 0.5 | 0.50 | 5.5 | 5.79 – 5.83 |
| M7 × 0.75 | 0.75 | 6.2 | 6.65 – 6.71 |
| M8 | 1.25 | 6.8 | 7.37 – 7.52 |
| M8 × 1 | 1.00 | 7.0 | 7.49 – 7.60 |
| M8 × 0.75 | 0.75 | 7.2 | 7.65 – 7.71 |
| M8 × 0.5 | 0.50 | 7.5 | 7.79 – 7.83 |
| M10 | 1.50 | 8.5 | 9.24 – 9.38 |
| M10 × 1.25 | 1.25 | 8.8 | 9.37 – 9.52 |
| M10 × 1 | 1.00 | 9.0 | 9.51 – 9.60 |
| M12 | 1.75 | 10.2 | 11.10 – 11.27 |
| M12 × 1.5 | 1.50 | 10.5 | 11.25 – 11.42 |
| M12 × 1.25 | 1.25 | 10.8 | 11.37 – 11.51 |
| M12 × 1 | 1.00 | 11.0 | 11.52 – 11.60 |
| M14 | 2.00 | 12.0 | 12.96 – 13.17 |
| M14 × 1.5 | 1.50 | 12.5 | 13.23 – 13.36 |
| M14 × 1.25 | 1.25 | 12.8 | 13.39 – 13.46 |
| M14 × 1 | 1.00 | 13.0 | 13.52 – 13.60 |
| M16 | 2.00 | 14.0 | 14.96 – 15.17 |
| M16 × 1.5 | 1.50 | 14.5 | 15.23 – 15.35 |
| M16 × 1 | 1.00 | 15.0 | 15.52 – 15.60 |
| M18 | 2.50 | 15.5 | 16.66 – 16.85 |
| M18 × 1.5 | 1.50 | 16.5 | 17.25 – 17.35 |
| M18 × 1 | 1.00 | 17.0 | 17.52 – 17.60 |
| M20 | 2.50 | 17.5 | 18.66 – 18.85 |
| M20 × 1.5 | 1.50 | 18.5 | 19.25 – 19.35 |
| M20 × 1 | 1.00 | 19.0 | 19.52 – 19.60 |
| M22 | 2.50 | 19.5 | 20.66 – 20.85 |
| M22 × 1.5 | 1.50 | 20.5 | 21.25 – 21.35 |
| M24 | 3.00 | 21.0 | 22.39 – 22.65 |
| M24 × 1.5 | 1.50 | 22.5 | 23.25 – 23.35 |
| M27 | 3.00 | 24.0 | 25.39 – 25.56 |
| M30 | 3.50 | 26.5 | 28.09 – 28.28 |
| M33 | 3.50 | 29.5 | 31.09 – 31.28 |
| M36 | 4.00 | 32.0 | 33.80 – 34.01 |
| M39 | 4.00 | 35.0 | 36.80 – 37.01 |
| M42 | 4.50 | 37.5 | 39.52 – 39.73 |
| M45 | 4.50 | 40.5 | 42.52 – 42.73 |
Clearance holes and counterbores for screws
| Screw | Clearance hole close / medium / free (mm) | Counterbore SHCS Ø × depth (mm) |
|---|---|---|
| M1.6 | 1.7 / 1.8 / 2 | — |
| M2 | 2.2 / 2.4 / 2.6 | — |
| M2.5 | 2.7 / 2.9 / 3.1 | — |
| M3 | 3.2 / 3.4 / 3.6 | 6.5 × 3.4 |
| M4 | 4.3 / 4.5 / 4.8 | 8 × 4.4 |
| M5 | 5.3 / 5.5 / 5.8 | 10 × 5.4 |
| M6 | 6.4 / 6.6 / 7 | 11 × 6.4 |
| M8 | 8.4 / 9 / 10 | 15 × 8.6 |
| M10 | 10.5 / 11 / 12 | 18 × 10.6 |
| M12 | 13 / 13.5 / 14.5 | 20 × 12.6 |
| M14 | 15 / 15.5 / 16.5 | — |
| M16 | 17 / 17.5 / 18.5 | 26 × 16.6 |
| M18 | 19 / 20 / 21 | — |
| M20 | 21 / 22 / 24 | 33 × 20.6 |
| M22 | 23 / 24 / 26 | — |
| M24 | 25 / 26 / 28 | 40 × 24.8 |
| M27 | 28 / 30 / 32 | — |
| M30 | 31 / 33 / 35 | — |
| M33 | 34 / 36 / 38 | — |
| M36 | 37 / 39 / 42 | 58 × 37 |
| M39 | 40 / 42 / 45 | — |
| M42 | 43 / 45 / 48 | — |
| M45 | 46 / 48 / 52 | — |
Clearance holes to ISO 273; counterbores for socket head cap screws (ISO 4762) to DIN 974-1, depth = head height + small allowance. Values checked against several published tables.
Every size, one page each
Coarse pitch
Fine pitch