# M42 tap drill size

The tap drill for an M42 × 4.5 metric coarse thread is 37.5 mm (1.4764 in). It leaves about 77 % thread, the normal range for steel.

## Drill options for M42 × 4.5

| Drill | Inch | Thread % |
|---|---|---|
| 37.3 mm | 1.4685 | 80 % |
| 37.4 mm | 1.4724 | 79 % |
| 37.5 mm | 1.4764 | 77 % |
| 37.6 mm | 1.4803 | 75 % |
| 37.7 mm | 1.4843 | 74 % |

## M42 thread data

- Thread: M42 × 4.5 (coarse)
- Pitch: 4.5 mm
- Tap drill: 37.5 mm (1.4764 in)
- Thread engagement: 77 %
- Clearance hole (ISO 273): 43 close, 45 normal, 48 loose (mm)

## Method

Thread % = 76.98 × (D − drill) / P = 76.98 × 4.5 / 4.5 = 77 %. Aim for 65–75 % in steel, 75–85 % in aluminium, brass and plastics.

## FAQ

**What size drill for an M42 × 4.5 tap?**
Use a 37.5 mm drill. It leaves about 77 % thread engagement.

**What is 37.5 mm in inches?**
37.5 mm is 1.4764 inch.

**What size clearance hole for M42?**
ISO 273 gives 43 mm for a close fit, 45 mm normal and 48 mm loose.

Source page: https://machinistcharts.com/tap-drill/m42/
Updated: 2026-10-05
Publisher: MachinistCharts (https://machinistcharts.com)