M22×2.5 thread

M22×2.5 is a coarse metric thread with a 22 mm (0.866") major diameter and 2.5 mm pitch. Tap it with a 19.5 mm drill; drill 23 mm to pass a bolt through.

The numbers

Designation

M22×2.5

Major diameter

22 mm / 0.866"

Minor diameter

19.294 mm

Pitch

2.5 mm pitch

Tap drill (75% thread)

19.5 mm — 19.5 mm

Clearance hole (close fit)

23 mm / 0.906"

Hex across flats

34 mm

How to measure what you have

1. Measure across the thread crests with calipers. A used M22×2.5 reads a little under 22 mm — the crests are truncated by the standard, then worn and plated, so anything from about 21.6 mm up is consistent with this size.
2. Measure the pitch: put a rule against the threads and count the distance over ten crests, then divide by ten. This one should give 2.5 mm.
3. A thread pitch gauge settles it in seconds and costs very little. Guessing between a coarse and a fine thread of the same diameter is the usual way a thread gets stripped.

Tightening torque

Plain steel property class 8.8 or SAE grade 5, dry threads, tightened to about 65% of yield. Lubricated threads reach the same preload at 20-30% less torque. Where the manufacturer publishes a figure — spark plugs, wheel nuts, cylinder heads — use theirs.

Where this size turns up

• Bridge and crane structural connections
• Large flange bolting
• Heavy plant pivot pins

ISO 4014:2011 gives 34 mm across flats. Older ISO and DIN 931 parts take a 32 mm spanner, so both exist in service.

Other threads at this diameter