# M24 tap drill size

The tap drill for an M24 × 3 metric coarse thread is 21 mm (0.8268 in). It leaves about 77 % thread, the normal range for steel.

## Drill options for M24 × 3

| Drill | Inch | Thread % |
|---|---|---|
| 20.8 mm | 0.8189 | 82 % |
| 20.9 mm | 0.8228 | 80 % |
| 21 mm | 0.8268 | 77 % |
| 21.1 mm | 0.8307 | 74 % |
| 21.2 mm | 0.8346 | 72 % |

## M24 thread data

- Thread: M24 × 3 (coarse)
- Pitch: 3 mm
- Tap drill: 21 mm (0.8268 in)
- Thread engagement: 77 %
- Clearance hole (ISO 273): 25 close, 26 normal, 28 loose (mm)

## Method

Thread % = 76.98 × (D − drill) / P = 76.98 × 3 / 3 = 77 %. Aim for 65–75 % in steel, 75–85 % in aluminium, brass and plastics.

## FAQ

**What size drill for an M24 × 3 tap?**
Use a 21 mm drill. It leaves about 77 % thread engagement.

**What is 21 mm in inches?**
21 mm is 0.8268 inch.

**What size clearance hole for M24?**
ISO 273 gives 25 mm for a close fit, 26 mm normal and 28 mm loose.

**How tight should an M24 bolt be?**
About 761 N·m for class 8.8 with dry threads.

Source page: https://machinistcharts.com/tap-drill/m24/
Updated: 2026-10-05
Publisher: MachinistCharts (https://machinistcharts.com)