---
title: "M14×1.25 tap drill 12.8 mm, clearance 15 mm"
description: "M14×1.25: tap drill 12.8 mm, clearance hole 15 mm, 21 mm hex. Full thread dimensions, how to identify it, and torque."
url: https://atoneplace.net/fastener/m14-1-25/
site: "At One Place"
---

# M14×1.25 thread

**M14×1.25 tap drill: 12.8 mm**

Clearance hole 15 mm · 21 mm hex

M14×1.25 is a fine metric thread with a 14 mm (0.551") major diameter and 1.25 mm pitch. Tap it with a 12.8 mm drill; drill 15 mm to pass a bolt through.

## The numbers

- **Designation:** M14×1.25
- **Major diameter:** 14 mm / 0.551"
- **Minor diameter:** 12.647 mm
- **Pitch:** 1.25 mm pitch
- **Tap drill (75% thread):** 12.8 mm — 12.8 mm
- **Clearance hole (close fit):** 15 mm / 0.591"
- **Hex across flats:** 21 mm

## How to measure what you have

1. Measure across the thread crests with calipers. A used M14×1.25 reads a little under 14 mm — the crests are truncated by the standard, then worn and plated, so anything from about 13.6 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 1.25 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: 127–171 N·m**

93.7–126.1 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

- Standard 14 mm automotive spark plugs
- Wheel studs on some Porsche and older European cars
- Glow plugs on some diesels

> The classic 14 mm automotive spark plug thread. Plugs are torqued to the plug maker’s figure, typically 20-30 Nm, not to the bolt figure quoted here.

## 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 |
| --- | --- | --- | --- |
| M14×2 | 2 mm | 12 mm | 15 mm |
| M14×1.5 | 1.5 mm | 12.5 mm | 15 mm |

## Common questions

### What size drill for an M14×1.25 tap?

12.8 mm (12.8 mm), which gives about 75% thread engagement.

### What clearance hole for M14×1.25?

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

### What spanner fits M14×1.25?

21 mm across the flats on a standard hex head.

## Related pages

- [M14×2](https://atoneplace.net/fastener/m14-2/)
- [M14×1.5](https://atoneplace.net/fastener/m14-1-5/)
- [M12×1.75](https://atoneplace.net/fastener/m12-1-75/)
- [M16×2](https://atoneplace.net/fastener/m16-2/)
- [M12×1.5](https://atoneplace.net/fastener/m12-1-5/)
- [M12×1.25](https://atoneplace.net/fastener/m12-1-25/)
- [M12×1](https://atoneplace.net/fastener/m12-1/)
- [M16×1.5](https://atoneplace.net/fastener/m16-1-5/)
- [M10×1.5](https://atoneplace.net/fastener/m10-1-5/)
- [M18×2.5](https://atoneplace.net/fastener/m18-2-5/)
- [M10×1.25](https://atoneplace.net/fastener/m10-1-25/)
- [M10×1](https://atoneplace.net/fastener/m10-1/)

## Sources

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