---
title: "M3.5×0.6 tap drill 2.9 mm, clearance 3.7 mm"
description: "M3.5×0.6: tap drill 2.9 mm, clearance hole 3.7 mm, 6 mm hex. Full thread dimensions, how to identify it, and torque."
url: https://atoneplace.net/fastener/m3-5-0-6/
site: "At One Place"
---

# M3.5×0.6 thread

**M3.5×0.6 tap drill: 2.9 mm**

Clearance hole 3.7 mm · 6 mm hex

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

**Typical torque: 1.7–2.3 N·m**

1.3–1.7 lb·ft

> 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

*Same diameter, different pitch. Forcing the wrong one strips the thread in a turn or two.*

| Thread | Pitch | Tap drill | Clearance |
| --- | --- | --- | --- |
| #6-32 UNC | 32 tpi | #36 | 3.8 mm |
| #6-40 UNF | 40 tpi | #33 | 3.8 mm |

## Common questions

### What size drill for an M3.5×0.6 tap?

2.9 mm (2.9 mm), which gives about 75% thread engagement.

### What clearance hole for M3.5×0.6?

3.7 mm for a close fit — enough to pass the bolt without slop.

### What spanner fits M3.5×0.6?

6 mm across the flats on a standard hex head.

## Related pages

- [#6-32 UNC](https://atoneplace.net/fastener/number-6-32/)
- [#6-40 UNF](https://atoneplace.net/fastener/number-6-40/)
- [M3×0.5](https://atoneplace.net/fastener/m3-0-5/)
- [M4×0.7](https://atoneplace.net/fastener/m4-0-7/)
- [M2.5×0.45](https://atoneplace.net/fastener/m2-5-0-45/)
- [M2×0.4](https://atoneplace.net/fastener/m2-0-4/)
- [M5×0.8](https://atoneplace.net/fastener/m5-0-8/)
- [M1.6×0.35](https://atoneplace.net/fastener/m1-6-0-35/)
- [M6×1](https://atoneplace.net/fastener/m6-1/)
- [M6×0.75](https://atoneplace.net/fastener/m6-0-75/)
- [M8×1.25](https://atoneplace.net/fastener/m8-1-25/)
- [M8×1](https://atoneplace.net/fastener/m8-1/)

## Sources

- Official vendor product documentation — At One Place (/about/)
- Typical range compiled from manufacturer specifications — At One Place (/about/)