Metric Thread Chart and Tap Drill Sizes
Look up ISO metric thread pitch (coarse and common fine), tap drill size and the M × 1.5 threads used for cable glands and instrument entries.
ISO metric threads
| Thread | Coarse pitch (mm) | Tap drill (mm) | Fine pitches (mm) |
|---|---|---|---|
| M3 | 0.50 | 2.50 | |
| M4 | 0.70 | 3.30 | |
| M5 | 0.80 | 4.20 | |
| M6 | 1.00 | 5.00 | |
| M8 | 1.25 | 6.75 | 1.0 |
| M10 | 1.50 | 8.50 | 1.25, 1.0 |
| M12 | 1.75 | 10.25 | 1.5, 1.25 |
| M14 | 2.00 | 12.00 | 1.5 |
| M16 | 2.00 | 14.00 | 1.5 |
| M20 | 2.50 | 17.50 | 1.5 |
| M24 | 3.00 | 21.00 | 2.0, 1.5 |
| M30 | 3.50 | 26.50 | 2.0 |
| M36 | 4.00 | 32.00 | 3.0 |
Metric Thread Basics
Designation: M20 (coarse), M20 × 1.5 (fine)
Cable gland and conduit entries on instruments and junction boxes normally use 1.5 mm pitch: M16 × 1.5, M20 × 1.5, M25 × 1.5, M32 × 1.5, M40 × 1.5, M50 × 1.5, M63 × 1.5.
Worked example
M20 × 1.5 is the most common instrument cable entry; its tap drill is 18.5 mm. M20 coarse has a 2.5 mm pitch and a 17.5 mm tap drill.
Frequently Asked Questions
What is the pitch of M20?
2.5 mm coarse; cable glands use M20 × 1.5 fine.
What drill size for M10?
8.5 mm for M10 coarse (1.5 mm pitch).
Which threads do cable glands use?
Metric fine M16 to M63 × 1.5, or NPT on North American equipment.
Learn more on the blog
Cable gland selection
A practical, field focused guide on instrumentationblog.in that explains the theory behind this tool and how engineers apply it on real plants.
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