Pitch Diameter from Three-Wire Measurement
The pitch diameter of a thread from the measurement read over three wires.
Example
You enter
- Thread standard inch
- Threads per inch (TPI) 13
- Measurement over 3 wires M (in) 0.49
You get
- Best wire 0.0444116
- Pitch diameter E 0.423383
Details, formula, and sources
E = M - 3W + 0.86603 x pitch. A 1/2-13 thread read at M = 0.4900 in over best wires gives E = 0.4234 in. Compare E to the thread-class limits for the fit. First-principles 60-degree geometry.
E = M - 3W + 0.86603 x P, the three-wire relation M = E + 3W - 0.86603 x P solved for the pitch diameter; best wire W = 0.57735 x P (range 0.560P to 0.650P) for a 60-degree thread.
The three-wire measurement-over-wires method for 60-degree threads solved for the pitch diameter, and the best-wire / 0.86603 constant - first-principles geometry as in Machinery's Handbook (Industrial Press), by name; public domain.
Pure geometry, public; compare the resulting pitch diameter E to the thread-class limits for the fit.
Estimate. AHJ and licensed professional govern.
Field names used by the API: thread_standard, tpi, measurement_over_wires_in, best_wire_in, pitch_diameter_in
- Thread form 60-degree included angle (UN / ISO metric); M is measured over three wiresthree-wire geometry