M8 × 1.25 Thread
The chart recommendation gives approximately 73.9% thread engagement — the conventional target for average materials. It is not the only valid choice; see the options below.
Specification
| Designation | M8 × 1.25 |
|---|---|
| Thread family | ISO metric coarse |
| Nominal size | M8 |
| Basic major diameter | 0.3150″ / 8 mm |
| Pitch | 1.25 mm |
| Recommended tap drill | 6.8 mm (0.2677″ / 6.8 mm) |
Tap drill options by thread engagement
Any of these standard drills produces a usable engagement for M8 × 1.25; smaller drills give stronger threads but higher tapping torque. Percentages use the conventional approximation (60° thread form).
| Drill | Decimal in | mm | Approx. engagement |
|---|---|---|---|
| G | 0.2610 | 6.629 | 84.4% |
| 6.7 mm | 0.2638 | 6.7 | 80.1% |
| 17/64″ | 0.2656 | 6.747 | 77.2% |
| H | 0.2660 | 6.756 | 76.6% |
| 6.8 mm — chart recommendation | 0.2677 | 6.8 | 73.9% |
| 6.9 mm | 0.2717 | 6.9 | 67.7% |
| I | 0.2720 | 6.909 | 67.2% |
| 7 mm | 0.2756 | 7 | 61.6% |
Nearest drills to the tap drill in other systems
| Drill | Size | vs 6.8 mm | Resulting engagement |
|---|---|---|---|
| 17/64″ | 0.2656″ / 6.747 mm | −0.053 mm | 77.2% |
| H | 0.2660″ / 6.756 mm | −0.044 mm | 76.6% |
Clearance holes
For a bolt or screw of this size to pass through freely. ISO 273 series (fine/medium/coarse), shown as close, normal, and loose.
Hex bolt & nut dimensions
For a standard hex bolt (ISO 4014/4017) and style-1 nut (ISO 4032) in this size.
| Wrench / socket size (bolt head) | 13 mm |
|---|---|
| Head height | 5.3 mm |
| Nut thickness | 6.8 mm |
| Compatible nut | M8 × 1.25 hex nut |
Basic (nominal) dimensions. See the wrench & socket size charts for all sizes and the metric ↔ SAE socket comparison.
Related threads
- M8 × 1 — same nominal size, 1 mm pitch (ISO metric fine) · compare
- M6 × 1 — next size down in metric-coarse
- M10 × 1.5 — next size up in metric-coarse