- Pitch
- 1.5 mm (coarse)
- Tap drill
- 8.5 mm (0.335 inch)
- Clearance hole (medium)
- 11 mm (0.433 inch)
- Pitch diameter
- 9.026 mm (0.355 inch)
- Minor diameter, bolt
- 8.16 mm (0.321 inch)
- Minor diameter, nut
- 8.376 mm (0.330 inch)
- Tensile stress area
- 58 mm²
Metric tap drill = size − pitch (about 75–80% thread). Check the drill your tap maker recommends for hard materials.
Metric coarse threads
| Thread | Pitch (mm) | Tap drill mm (inch) | Clearance hole mm (inch) | Stress area (mm²) |
|---|---|---|---|---|
| M1.6 | 0.35 | 1.25 (0.0492) | 1.8 (0.0709) | 1.3 |
| M2 | 0.4 | 1.6 (0.0630) | 2.4 (0.0945) | 2.1 |
| M2.5 | 0.45 | 2.05 (0.0807) | 2.9 (0.114) | 3.4 |
| M3 | 0.5 | 2.5 (0.0984) | 3.4 (0.134) | 5 |
| M4 | 0.7 | 3.3 (0.130) | 4.5 (0.177) | 8.8 |
| M5 | 0.8 | 4.2 (0.165) | 5.5 (0.217) | 14.2 |
| M6 | 1 | 5 (0.197) | 6.6 (0.260) | 20.1 |
| M8 | 1.25 | 6.75 (0.266) | 9 (0.354) | 36.6 |
| M10 | 1.5 | 8.5 (0.335) | 11 (0.433) | 58 |
| M12 | 1.75 | 10.25 (0.404) | 13.5 (0.531) | 84.3 |
| M14 | 2 | 12 (0.472) | 15.5 (0.610) | 115.4 |
| M16 | 2 | 14 (0.551) | 17.5 (0.689) | 156.7 |
| M18 | 2.5 | 15.5 (0.610) | 20 (0.787) | 192.5 |
| M20 | 2.5 | 17.5 (0.689) | 22 (0.866) | 244.8 |
| M22 | 2.5 | 19.5 (0.768) | 24 (0.945) | 303.4 |
| M24 | 3 | 21 (0.827) | 26 (1.02) | 352.5 |
| M27 | 3 | 24 (0.945) | 30 (1.18) | 459.4 |
| M30 | 3.5 | 26.5 (1.04) | 33 (1.30) | 560.6 |
| M33 | 3.5 | 29.5 (1.16) | 36 (1.42) | 693.6 |
| M36 | 4 | 32 (1.26) | 39 (1.54) | 816.7 |
| M39 | 4 | 35 (1.38) | 42 (1.65) | 975.8 |
| M42 | 4.5 | 37.5 (1.48) | 45 (1.77) | 1120.9 |
| M45 | 4.5 | 40.5 (1.59) | 48 (1.89) | 1306 |
| M48 | 5 | 43 (1.69) | 52 (2.05) | 1473.1 |
| M52 | 5 | 47 (1.85) | 56 (2.20) | 1757.8 |
| M56 | 5.5 | 50.5 (1.99) | 62 (2.44) | 2030 |
| M60 | 5.5 | 54.5 (2.15) | 66 (2.60) | 2362 |
| M64 | 6 | 58 (2.28) | 70 (2.76) | 2676 |
Metric fine threads
| Thread | Tap drill mm (inch) | Stress area (mm²) |
|---|---|---|
| M8 × 1 | 7 (0.276) | 39.2 |
| M10 × 1.25 | 8.75 (0.344) | 61.2 |
| M10 × 1 | 9 (0.354) | 64.5 |
| M12 × 1.5 | 10.5 (0.413) | 88.1 |
| M12 × 1.25 | 10.75 (0.423) | 92.1 |
| M14 × 1.5 | 12.5 (0.492) | 124.5 |
| M16 × 1.5 | 14.5 (0.571) | 167.2 |
| M18 × 1.5 | 16.5 (0.650) | 216.2 |
| M20 × 1.5 | 18.5 (0.728) | 271.5 |
| M22 × 1.5 | 20.5 (0.807) | 333.1 |
| M24 × 2 | 22 (0.866) | 384.4 |
| M27 × 2 | 25 (0.984) | 495.7 |
| M30 × 2 | 28 (1.10) | 621.2 |
| M33 × 2 | 31 (1.22) | 760.8 |
| M36 × 3 | 33 (1.30) | 864.9 |
| M39 × 3 | 36 (1.42) | 1028.4 |
| M42 × 3 | 39 (1.54) | 1206 |
| M45 × 3 | 42 (1.65) | 1397.7 |
| M48 × 3 | 45 (1.77) | 1603.6 |
| M52 × 4 | 48 (1.89) | 1828.2 |
| M56 × 4 | 52 (2.05) | 2144 |
| M60 × 4 | 56 (2.20) | 2484.8 |
| M64 × 4 | 60 (2.36) | 2850.8 |
BSP parallel pipe threads (G)
| Size | TPI | Pitch (mm) | Major dia. mm (inch) | Tap drill mm (inch) |
|---|---|---|---|---|
| G 1/8 | 28 | 0.907 | 9.728 (0.383) | 8.8 (0.346) |
| G 1/4 | 19 | 1.337 | 13.157 (0.518) | 11.8 (0.465) |
| G 3/8 | 19 | 1.337 | 16.662 (0.656) | 15.25 (0.600) |
| G 1/2 | 14 | 1.814 | 20.955 (0.825) | 19 (0.748) |
| G 3/4 | 14 | 1.814 | 26.441 (1.04) | 24.5 (0.965) |
| G 1 | 11 | 2.309 | 33.249 (1.31) | 30.75 (1.21) |
| G 1 1/4 | 11 | 2.309 | 41.91 (1.65) | 39.5 (1.56) |
| G 1 1/2 | 11 | 2.309 | 47.803 (1.88) | 45.25 (1.78) |
| G 2 | 11 | 2.309 | 59.614 (2.35) | 57 (2.24) |
Good to know
- Metric tap drill = size − pitch; for roll (forming) taps the drill is larger, about size − pitch/2
- Coarse threads are the default; write the pitch only for fine threads (M12 × 1.5)
- BSP parallel (G) seals with a washer or O-ring; BSP taper (R/Rc) seals on the thread
- Stress area is used to work out the load a bolt can carry
Questions
- What is the tap drill size for M10?
- 8.5 mm (0.335 inch) for M10 coarse (1.5 mm (0.0591 inch) pitch). For M10 × 1.25 fine it is 8.75 mm (0.344 inch), and for M10 × 1 it is 9 mm (0.354 inch). The rule is: tap drill = thread size − pitch.
- What is the pitch of M12?
- M12 coarse has a 1.75 mm (0.0689 inch) pitch. The common fine pitches are 1.5 mm (0.0591 inch) and 1.25 mm (0.0492 inch), written M12 × 1.5 and M12 × 1.25.
- What is the clearance hole for an M8 bolt?
- 9 mm (0.354 inch) is the medium clearance hole for M8 (ISO 273). Use 8.4 mm (0.331 inch) for a close fit and 10 mm (0.394 inch) for a loose one.
- What is the tap drill for 1/2 inch BSP?
- About 19 mm (0.748 inch) for G 1/2 (BSP parallel, 14 threads per inch). G 1/4 needs about 11.8 mm (0.465 inch) and G 3/8 about 15.25 mm (0.600 inch).
Need threading done? See drilling, boring and tapping and thread rolling.
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Get startedDimensions from ISO 261/724 (metric), ISO 228-1 (BSP) and ISO 273 (clearance holes). Tap drills are the usual workshop sizes; follow your tap maker for special materials.