Metric fine
Tap drill 16 mm for a M18 × 2.0 thread — major Ø 18 mm, pitch 2 mm (12.7 TPI).
Profile
| Designation | M18 × 2.0 |
|---|---|
| Major (outside) diameter | 18 mm · 0.7087" |
| Pitch | 2 mm · 12.7 TPI |
| Pitch diameter | 16.701 mm · 0.6575" |
| Minor diameter (external) | 15.546 mm · 0.6121" |
| Minor diameter (internal) | 15.835 mm · 0.6234" |
| Recommended tap drill | 16 mm · ≈77% thread |
| Clearance hole | Close 19 · Normal 20 · Loose 21 mm |
| Hex head (across flats) | 27 mm |
| Socket key (across flats) | 14 mm |
ISO 273 clearance holes (fine / medium / coarse).
Target preload is 75% of proof load; torque is estimated from T = K · F · d.
| Grade / class | Stress area | Preload | Torque |
|---|---|---|---|
| Class 8.8 | 204.2 mm² | 88.82 kN | 319.7 N·m |
| Class 10.9 | 204.2 mm² | 127.1 kN | 457.6 N·m |
| Class 12.9 | 204.2 mm² | 148.54 kN | 534.7 N·m |
For a M18 × 2.0 thread, drill the hole with a 16 mm tap drill (16 mm — the standard D − P rule) before tapping. That produces roughly 77% thread engagement, the usual target for a strong, tappable hole. The mating bolt has a major diameter of 18 mm and a pitch of 2 mm (12.7 TPI).
To pass a M18 × 2.0 bolt through a part rather than thread it, use a clearance hole: Close 19 · Normal 20 · Loose 21 mm.
All values are generated from the standard thread formulas (ISO 68-1 / ASME B1.1) and published standard tables — not hand-entered. See the full reference.
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