With a 16 TPI leadscrew and the standard 7x gear set (20, 20, 30, 35, 40, 40, 45, 50, 55, 57, 60, 65, 80), every common inch thread from 8 to 56 TPI has an exact train, and common metric pitches come within about a tenth of a percent.
These trains are computed, not copied from a manufacturer chart, assuming the first change gear turns 1:1 with the spindle, which is the standard 7x arrangement. Check them against the chart on your own machine before cutting; some variants add an internal reduction. Physical fit on the banjo is not checked.
For any other thread, leadscrew or gear set, use the change gear calculator.
Tools that go with this chart
Inch threads (A drives B; C on the same stud as B drives D on the leadscrew)
| TPI | A | B | C | D | Actual TPI | Error |
|---|---|---|---|---|---|---|
| 8 | 20 | 20 | 60 | 30 | 8.000 | 0.000% |
| 9 | 40 | 20 | 40 | 45 | 9.000 | 0.000% |
| 10 | 40 | 20 | 40 | 50 | 10.000 | 0.000% |
| 11 | 40 | 20 | 40 | 55 | 11.000 | 0.000% |
| 12 | 20 | 20 | 40 | 30 | 12.000 | 0.000% |
| 13 | 40 | 20 | 40 | 65 | 13.000 | 0.000% |
| 14 | 20 | 20 | 40 | 35 | 14.000 | 0.000% |
| 16 | 20 | 20 | 40 | 40 | 16.000 | 0.000% |
| 18 | 20 | 20 | 40 | 45 | 18.000 | 0.000% |
| 19 | 40 | 50 | 60 | 57 | 19.000 | 0.000% |
| 20 | 20 | 20 | 40 | 50 | 20.000 | 0.000% |
| 24 | 20 | 20 | 30 | 45 | 24.000 | 0.000% |
| 26 | 20 | 20 | 40 | 65 | 26.000 | 0.000% |
| 27 | 20 | 30 | 40 | 45 | 27.000 | 0.000% |
| 28 | 20 | 35 | 40 | 40 | 28.000 | 0.000% |
| 32 | 20 | 20 | 30 | 60 | 32.000 | 0.000% |
| 36 | 20 | 40 | 40 | 45 | 36.000 | 0.000% |
| 40 | 20 | 40 | 40 | 50 | 40.000 | 0.000% |
| 44 | 20 | 40 | 40 | 55 | 44.000 | 0.000% |
| 48 | 20 | 30 | 20 | 40 | 48.000 | 0.000% |
| 56 | 20 | 35 | 20 | 40 | 56.000 | 0.000% |
Metric pitches on an inch leadscrew (approximate)
| Pitch (mm) | A | B | C | D | Actual pitch (mm) | Error |
|---|---|---|---|---|---|---|
| 0.5 | 20 | 57 | 45 | 50 | 0.5013 | 0.262% |
| 0.7 | 35 | 55 | 45 | 65 | 0.6994 | 0.087% |
| 0.75 | 35 | 57 | 50 | 65 | 0.7498 | 0.022% |
| 0.8 | 30 | 55 | 60 | 65 | 0.7993 | 0.087% |
| 1 | 45 | 55 | 50 | 65 | 0.9991 | 0.087% |
| 1.25 | 35 | 40 | 45 | 50 | 1.2502 | 0.012% |
| 1.5 | 40 | 50 | 65 | 55 | 1.5009 | 0.061% |
| 1.75 | 40 | 35 | 55 | 57 | 1.7506 | 0.036% |
| 2 | 40 | 35 | 55 | 50 | 1.9957 | 0.215% |
| 2.5 | 35 | 20 | 45 | 50 | 2.5003 | 0.012% |
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Frequently asked questions
Can I cut metric threads on an inch mini lathe?
Yes, to within a small fraction of a percent with the standard gears, which is fine for short threads and nuts you fit to the part. For long metric threads that must mate commercial parts, a 127 tooth transposing gear or a lathe with a metric leadscrew gives exact pitches.
Keep going
Figures are from published standards and handbook values, reproduced for convenience. Check critical dimensions against the standard or your tooling manufacturer.