M8 × 1.25 Tap Drill Size & Thread Specs
Everything for a M8 × 1.25 coarse pitch thread on one page: tap drill (6.8 mm), clearance holes, wrench and hex key sizes, and the nearest inch thread.
SP-TD-01 · M8 × 1.25
M8 × 1.25 specs
SizePlate
M8 × 1.25 · tap with
6.8 mm drill
.2677″
6.8 mm · 74% thread
- Inch drill
- H · .2660
- Clearance
- 8.4 / 9 mm
- Wrench
- 13 mm
- Cap screw key
- 6 mm
Thread
- Nominal size
- M8 · .3150″
- Pitch
- 1.25 mm · 20.3 TPI
- Series
- coarse
- fine pitch
- M8 × 1.0
Drilling
- Tap drill
- 6.8 mm · .2677
- Inch substitute
- H · .2660
- Close fit
- 8.4 mm
- Normal fit
- 9 mm
- Free fit
- 10 mm
Tools
- Hex head (ISO 4017)
- 13 mm
- Hex head (DIN 933)
- 13 mm
- Socket head cap key
- 6 mm
- Button head key
- 5 mm
- Flat head key
- 5 mm
Nearest inch
- Thread
- 5/16-18
- Major diameter
- .3125″
- Threads per inch
- 18
- Tap drill
- F
- Interchangeable
- No
Not interchangeable means the threads look close but won't run together: forcing one into the other strips both.
Drill size by thread percentage
Larger drill, less thread, easier tapping. 75% is the usual target.
| Drill | Decimal | mm | Thread |
|---|---|---|---|
| G | .2610 | 6.63 | 84% |
| 6.7 mm | .2638 | 6.7 | 80% |
| 17/64 | .2656 | 6.75 | 77% |
| H | .2660 | 6.76 | 77% |
| 6.8 mm | .2677 | 6.8 | 74% |
| 6.9 mm | .2717 | 6.9 | 68% |
| I | .2720 | 6.91 | 67% |
| 7 mm | .2756 | 7 | 62% |
| J | .2770 | 7.04 | 59% |
| 7.1 mm | .2795 | 7.1 | 55% |
| K | .2810 | 7.14 | 53% |
| 9/32 | .2813 | 7.15 | 53% |
| 7.2 mm | .2835 | 7.2 | 49% |
Neighboring sizes
- M5 × 0.5tap 4.5 mm
- M6 × 1.0tap 5 mm
- M6 × 0.75tap 5.2 mm
- M8 × 1.0tap 7 mm
- M10 × 1.5tap 8.5 mm
- M10 × 1.25tap 8.8 mm
Questions
What does M8 × 1.25 mean?
An ISO metric thread with a 8 mm major diameter and a 1.25 mm pitch (the distance from one thread crest to the next). It’s the coarse pitch for M8.
Can I use a H drill instead?
Usually. H is .2660″ against .2677″ for the 6.8 mm drill, which changes the thread engagement by a few percent at most.