M27×3 thread

M27×3 is a coarse metric thread with a 27 mm (1.063") major diameter and 3 mm pitch. Tap it with a 24 mm drill; drill 28 mm to pass a bolt through.

The numbers

Designation

M27×3

Major diameter

27 mm / 1.063"

Minor diameter

23.752 mm

Pitch

3 mm pitch

Tap drill (75% thread)

24 mm — 24 mm

Clearance hole (close fit)

28 mm / 1.102"

Hex across flats

41 mm

How to measure what you have

1. Measure across the thread crests with calipers. A used M27×3 reads a little under 27 mm — the crests are truncated by the standard, then worn and plated, so anything from about 26.6 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 3 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

• Heavy structural connections
• Large flange and pressure-vessel bolting
• Mining and quarry plant

Other threads at this diameter