Last updated 10 August 2026
No. The multiplier scales with the flank angle: a 29 degree ACME thread shifts pitch diameter about 8.9 times the per-side thickness, against 4 for a 60 degree UN form.
The four times figure is specific to a 60 degree flank. The general rule is that the shift scales as the tangent of thirty degrees over the tangent of half the flank angle, so a shallower flank moves pitch diameter further per unit of coating. Whitworth at 55 degrees comes out near 4.4, trapezoidal at 30 degrees near 8.6, ACME at 29 degrees near 8.9.
A shop that applies the 60 degree rule to an ACME lead screw leaves less than half the correction it needed, and the part comes back from plating with a thread that will not assemble.
| Flank angle | Thread forms | Pitch diameter shift, both-sided | One-sided |
|---|---|---|---|
| none, a plain diameter | any | 2 | 1 |
| 60 degrees | UN, UNC, UNF, ISO metric | 4 | 2 |
| 55 degrees | Whitworth, BSP, BSPT | 4.436 | 2.218 |
| 30 degrees | Trapezoidal, Tr | 8.619 | 4.309 |
| 29 degrees | ACME, Stub ACME | 8.93 | 4.465 |
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Pitch diameter shift per unit of coating thickness, by thread flank angle. MIL-STD-870, Federal Screw Thread Specification H28. CC-BY-4.0, attribute to ctrlPlanner.