ISO Metric Coarse Thread · DIN 13-1 / ISO 261
M18 Thread: Pitch, Tap Drill & Dimensions
M18 is an ISO metric coarse thread with a 2.5 mm pitch. The tap drill is 15.5 mm, and the internal minor diameter D1 is 15.294 mm.
| Nominal (major) diameter | 18 mm |
|---|---|
| Pitch | 2.5 mm (coarse) |
| Tap drill (D − P) | 15.5 mm |
| Pitch diameter d2 / D2 | 16.376 mm |
| Minor diameter, external d3 | 14.933 mm |
| Minor diameter, internal D1 | 15.294 mm |
| Thread depth, external h3 | 1.533 mm |
| Flank angle | 60° |
| Clearance hole (fine / medium / coarse) | 19 / 20 / 21 mm |
| Hex spanner size (ISO 4032) | 27 mm |
| Socket cap screw hex key (ISO 4762) | 14 mm |
Common questions
What size drill do I use to tap M18?
Use a 15.5 mm drill. This is the standard tap drill for M18; for hard materials or deep threads a slightly larger drill reduces tapping torque.
What is the pitch of M18?
The pitch of M18 is 2.5 mm (coarse), meaning the thread advances that distance in one full turn.
Where can I find other ISO Metric Coarse Thread sizes?
The full ISO Metric Coarse Thread table, with every size and a live filter, is on its standard page, and the Thread Finder searches all 73 standards at once.
Reference values; computed values use the ISO basic profile. Verify against the current standard before production use.