# M30 tap drill size

The tap drill for an M30 × 3.5 metric coarse thread is 26.5 mm (1.0433 in). It leaves about 77 % thread, the normal range for steel.

## Drill options for M30 × 3.5

| Drill | Inch | Thread % |
|---|---|---|
| 26.3 mm | 1.0354 | 81 % |
| 26.4 mm | 1.0394 | 79 % |
| 26.5 mm | 1.0433 | 77 % |
| 26.6 mm | 1.0472 | 75 % |
| 26.7 mm | 1.0512 | 73 % |

## M30 thread data

- Thread: M30 × 3.5 (coarse)
- Pitch: 3.5 mm
- Tap drill: 26.5 mm (1.0433 in)
- Thread engagement: 77 %
- Clearance hole (ISO 273): 31 close, 33 normal, 35 loose (mm)

## Method

Thread % = 76.98 × (D − drill) / P = 76.98 × 3.5 / 3.5 = 77 %. Aim for 65–75 % in steel, 75–85 % in aluminium, brass and plastics.

## FAQ

**What size drill for an M30 × 3.5 tap?**
Use a 26.5 mm drill. It leaves about 77 % thread engagement.

**What is 26.5 mm in inches?**
26.5 mm is 1.0433 inch.

**What size clearance hole for M30?**
ISO 273 gives 31 mm for a close fit, 33 mm normal and 35 mm loose.

**How tight should an M30 bolt be?**
About 1,514 N·m for class 8.8 with dry threads.

Source page: https://machinistcharts.com/tap-drill/m30/
Updated: 2026-10-05
Publisher: MachinistCharts (https://machinistcharts.com)