M1.6×0.35 thread

M1.6×0.35 is a coarse metric thread with a 1.6 mm (0.063") major diameter and 0.35 mm pitch. Tap it with a 1.25 mm drill; drill 1.7 mm to pass a bolt through.

The numbers

Designation

M1.6×0.35

Major diameter

1.6 mm / 0.063"

Minor diameter

1.221 mm

Pitch

0.35 mm pitch

Tap drill (75% thread)

1.25 mm — 1.25 mm

Clearance hole (close fit)

1.7 mm / 0.067"

Hex across flats

3.2 mm

How to measure what you have

1. Measure across the thread crests with calipers. A used M1.6×0.35 reads a little under 1.6 mm — the crests are truncated by the standard, then worn and plated, so anything from about 1.2 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 0.35 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

No torque figure is given for this size. Small and fine threads like this are generally not supplied to a strength grade, and in most assemblies the tapped material strips before the fastener yields — so a published bolt torque would be the wrong limit to work to. Tighten to snug plus a small turn, or use the figure the manufacturer of the part specifies.

Where this size turns up

• Spectacle hinge and temple screws
• Terminal screws in small relays and connectors
• Watch case backs and strap bars