# M1.6 tap drill size

The tap drill for an M1.6 × 0.35 metric coarse thread is 1.25 mm (0.0492 in). It leaves about 77 % thread, the normal range for steel.

## Drill options for M1.6 × 0.35

| Drill | Inch | Thread % |
|---|---|---|
| 1.15 mm | 0.0453 | 99 % |
| 1.25 mm | 0.0492 | 77 % |
| 1.35 mm | 0.0531 | 55 % |

## M1.6 thread data

- Thread: M1.6 × 0.35 (coarse)
- Pitch: 0.35 mm
- Tap drill: 1.25 mm (0.0492 in)
- Thread engagement: 77 %
- Clearance hole (ISO 273): 1.7 close, 1.8 normal, 2 loose (mm)

## Method

Thread % = 76.98 × (D − drill) / P = 76.98 × 0.35 / 0.35 = 77 %. Aim for 65–75 % in steel, 75–85 % in aluminium, brass and plastics.

## FAQ

**What size drill for an M1.6 × 0.35 tap?**
Use a 1.25 mm drill. It leaves about 77 % thread engagement.

**What is 1.25 mm in inches?**
1.25 mm is 0.0492 inch.

**What size clearance hole for M1.6?**
ISO 273 gives 1.7 mm for a close fit, 1.8 mm normal and 2 mm loose.

Source page: https://machinistcharts.com/tap-drill/m1-6/
Updated: 2026-10-05
Publisher: MachinistCharts (https://machinistcharts.com)