# M8x1 tap drill size

The tap drill for an M8 × 1 metric fine thread is 7 mm (0.2756 in). It leaves about 77 % thread, the normal range for steel.

## Drill options for M8 × 1

| Drill | Inch | Thread % |
|---|---|---|
| 6.8 mm | 0.2677 | 92 % |
| 6.9 mm | 0.2717 | 85 % |
| 7 mm | 0.2756 | 77 % |
| 7.1 mm | 0.2795 | 69 % |
| 7.2 mm | 0.2835 | 62 % |

## M8x1 thread data

- Thread: M8 × 1 (fine)
- Pitch: 1 mm
- Tap drill: 7 mm (0.2756 in)
- Thread engagement: 77 %
- Clearance hole (ISO 273): 8.4 close, 9 normal, 10 loose (mm)

## Method

Thread % = 76.98 × (D − drill) / P = 76.98 × 1 / 1 = 77 %. Aim for 65–75 % in steel, 75–85 % in aluminium, brass and plastics.

## FAQ

**What size drill for an M8 × 1 tap?**
Use a 7 mm drill. It leaves about 77 % thread engagement.

**What is 7 mm in inches?**
7 mm is 0.2756 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/m8x1/
Updated: 2026-10-05
Publisher: MachinistCharts (https://machinistcharts.com)