UNM miniature threads: pitch and tap drill chart
Full chart with the tap drill for every size. Press “Calculate” on any row to open the calculator with that thread.
UNM (Unified Miniature, ASME B1.10M) are threads from 0.30 to 1.40 mm for watchmaking, instruments, optics and electronics. They are designated by the diameter in millimetres ("0.80 UNM") and the pitch is also in millimetres. At these sizes the drill is D − P rounded to the hundredth, because micro drills come in 0.01 mm steps.
| Thread | Pitch (mm) | Major Ø (mm) | Tap drill | Calculate |
|---|---|---|---|---|
| 0.30 UNM | 0.08 | 0.3 | ⌀ 0.22 | |
| 0.35 UNM | 0.09 | 0.35 | ⌀ 0.26 | |
| 0.40 UNM | 0.1 | 0.4 | ⌀ 0.3 | |
| 0.45 UNM | 0.1 | 0.45 | ⌀ 0.35 | |
| 0.50 UNM | 0.125 | 0.5 | ⌀ 0.38 | |
| 0.55 UNM | 0.125 | 0.55 | ⌀ 0.43 | |
| 0.60 UNM | 0.15 | 0.6 | ⌀ 0.45 | |
| 0.70 UNM | 0.175 | 0.7 | ⌀ 0.53 | |
| 0.80 UNM | 0.2 | 0.8 | ⌀ 0.6 | |
| 0.90 UNM | 0.225 | 0.9 | ⌀ 0.68 | |
| 1.00 UNM | 0.25 | 1 | ⌀ 0.75 | |
| 1.10 UNM | 0.25 | 1.1 | ⌀ 0.85 | |
| 1.20 UNM | 0.25 | 1.2 | ⌀ 0.95 | |
| 1.40 UNM | 0.3 | 1.4 | ⌀ 1.1 |
How to read the chart
Drill: D − P, rounded to the hundredth. At these diameters a 0.02 mm difference changes the thread percentage a lot, so a micro drill of the exact size is used.
Pitch: in millimetres, as in the designation ("0.80 UNM" has a 0.2 mm pitch).
"Calculate" opens the calculator with that size. Guide values; with threads this small, check against the tap data sheet and with a gauge.
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