M24×3 thread

M24×3 is a coarse metric thread with a 24 mm (0.945") major diameter and 3 mm pitch. Tap it with a 21 mm drill; drill 25 mm to pass a bolt through.

The numbers

Designation

M24×3

Major diameter

24 mm / 0.945"

Minor diameter

20.752 mm

Pitch

3 mm pitch

Tap drill (75% thread)

21 mm — 21 mm

Clearance hole (close fit)

25 mm / 0.984"

Hex across flats

36 mm

How to measure what you have

1. Measure across the thread crests with calipers. A used M24×3 reads a little under 24 mm — the crests are truncated by the standard, then worn and plated, so anything from about 23.6 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

• Structural steel column splices
• Wind turbine and tower flange bolting
• Large pressure-vessel and pipe flanges

Other threads at this diameter