# M8 tap drill size

The tap drill for an M8 × 1.25 metric coarse thread is 6.8 mm (0.2677 in). It leaves about 74 % thread, the normal range for steel.

## Drill options for M8 × 1.25

| Drill | Inch | Thread % |
|---|---|---|
| 6.6 mm | 0.2598 | 86 % |
| 6.7 mm | 0.2638 | 80 % |
| 6.8 mm | 0.2677 | 74 % |
| 6.9 mm | 0.2717 | 68 % |
| 7 mm | 0.2756 | 62 % |

## M8 thread data

- Thread: M8 × 1.25 (coarse)
- Pitch: 1.25 mm
- Tap drill: 6.8 mm (0.2677 in)
- Thread engagement: 74 %
- Clearance hole (ISO 273): 8.4 close, 9 normal, 10 loose (mm)

## Method

Thread % = 76.98 × (D − drill) / P = 76.98 × 1.2 / 1.25 = 74 %. Aim for 65–75 % in steel, 75–85 % in aluminium, brass and plastics.

## FAQ

**What size drill for an M8 × 1.25 tap?**
Use a 6.8 mm drill. It leaves about 74 % thread engagement.

**What is 6.8 mm in inches?**
6.8 mm is 0.2677 inch.

**What size clearance hole for M8?**
ISO 273 gives 8.4 mm for a close fit, 9 mm normal and 10 mm loose.

**How tight should an M8 bolt be?**
About 25 N·m for class 8.8 with dry threads.

Source page: https://machinistcharts.com/tap-drill/m8/
Updated: 2026-10-05
Publisher: MachinistCharts (https://machinistcharts.com)