M3.5×0.6 thread

M3.5×0.6 is a coarse metric thread with a 3.5 mm (0.138") major diameter and 0.6 mm pitch. Tap it with a 2.9 mm drill; drill 3.7 mm to pass a bolt through.

The numbers

Designation

M3.5×0.6

Major diameter

3.5 mm / 0.138"

Minor diameter

2.85 mm

Pitch

0.6 mm pitch

Tap drill (75% thread)

2.9 mm — 2.9 mm

Clearance hole (close fit)

3.7 mm / 0.146"

Hex across flats

6 mm

How to measure what you have

1. Measure across the thread crests with calipers. A used M3.5×0.6 reads a little under 3.5 mm — the crests are truncated by the standard, then worn and plated, so anything from about 3.1 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 0.6 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

• UK and Irish wall socket and light switch faceplate screws
• Consumer-unit and back-box lugs
• Older appliance chassis screws

The thread on UK and Irish socket, switch and light-fitting faceplate screws, which go into a 3.5 mm lug in the back box.

Other threads at this diameter