Three-Wire Thread Measurement
Three-wire measurement over a 60-degree thread.
Example
You enter
- Thread standard inch
- Threads per inch (TPI) 13
- Pitch diameter E (in) 0.45
You get
- Best wire 0.0444116
- Measurement over 3 wires 0.516617
Checked against published worked examples from: U.S. Navy, Naval Education and Training Command; Osborn Products, Inc.
Details, formula, and sources
ScopeBest wire W = 0.57735 x pitch, acceptable wire range, and measurement over three wires M = E + 3W - 0.86603 x pitch from the user-supplied pitch diameter (first-principles thread geometry).
Formula or tableBest wire W = P / (2 cos30) = 0.57735 x P (usable range 0.505182P to 1.010362P, ASME B1.2 limits as printed in the Osborn three-wire catalog; 0.650013P is the 29-degree Acme maximum); measurement over three wires M = E + 3W - 0.86603 x P for a 60-degree thread.
Source and editionThe three-wire measurement-over-wires method for 60-degree threads and the best-wire / 0.86603 constant - first-principles geometry as in Machinery's Handbook (Industrial Press), by name; public domain.
Free accessPure geometry, public; the pitch diameter E is user-supplied (no thread-class table lookup here).
What governsEstimate. AHJ and licensed professional govern.
API field namesthread_standard, tpi, pitch_diameter_in, best_wire_in, measurement_over_wires_in
- Thread form 60-degree included angle (UN / ISO metric); the pitch diameter E is user-suppliedthree-wire geometry