# M3 tap drill size

The tap drill for an M3 × 0.5 metric coarse thread is 2.5 mm (0.0984 in). It leaves about 77 % thread, the normal range for steel.

## Drill options for M3 × 0.5

| Drill | Inch | Thread % |
|---|---|---|
| 2.4 mm | 0.0945 | 92 % |
| 2.5 mm | 0.0984 | 77 % |
| 2.6 mm | 0.1024 | 62 % |
| 2.7 mm | 0.1063 | 46 % |

## M3 thread data

- Thread: M3 × 0.5 (coarse)
- Pitch: 0.5 mm
- Tap drill: 2.5 mm (0.0984 in)
- Thread engagement: 77 %
- Clearance hole (ISO 273): 3.2 close, 3.4 normal, 3.6 loose (mm)

## Method

Thread % = 76.98 × (D − drill) / P = 76.98 × 0.5 / 0.5 = 77 %. Aim for 65–75 % in steel, 75–85 % in aluminium, brass and plastics.

## FAQ

**What size drill for an M3 × 0.5 tap?**
Use a 2.5 mm drill. It leaves about 77 % thread engagement.

**What is 2.5 mm in inches?**
2.5 mm is 0.0984 inch.

**What size clearance hole for M3?**
ISO 273 gives 3.2 mm for a close fit, 3.4 mm normal and 3.6 mm loose.

Source page: https://machinistcharts.com/tap-drill/m3/
Updated: 2026-10-05
Publisher: MachinistCharts (https://machinistcharts.com)