# M20x1.5 tap drill size

The tap drill for an M20 × 1.5 metric fine thread is 18.5 mm (0.7283 in). It leaves about 77 % thread, the normal range for steel.

## Drill options for M20 × 1.5

| Drill | Inch | Thread % |
|---|---|---|
| 18.3 mm | 0.7205 | 87 % |
| 18.4 mm | 0.7244 | 82 % |
| 18.5 mm | 0.7283 | 77 % |
| 18.6 mm | 0.7323 | 72 % |
| 18.7 mm | 0.7362 | 67 % |

## M20x1.5 thread data

- Thread: M20 × 1.5 (fine)
- Pitch: 1.5 mm
- Tap drill: 18.5 mm (0.7283 in)
- Thread engagement: 77 %
- Clearance hole (ISO 273): 21 close, 22 normal, 24 loose (mm)

## Method

Thread % = 76.98 × (D − drill) / P = 76.98 × 1.5 / 1.5 = 77 %. Aim for 65–75 % in steel, 75–85 % in aluminium, brass and plastics.

## FAQ

**What size drill for an M20 × 1.5 tap?**
Use a 18.5 mm drill. It leaves about 77 % thread engagement.

**What is 18.5 mm in inches?**
18.5 mm is 0.7283 inch.

**What size clearance hole for M20?**
ISO 273 gives 21 mm for a close fit, 22 mm normal and 24 mm loose.

**How tight should an M20 bolt be?**
About 441 N·m for class 8.8 with dry threads.

Source page: https://machinistcharts.com/tap-drill/m20x1-5/
Updated: 2026-10-05
Publisher: MachinistCharts (https://machinistcharts.com)