Thread Rolling Blank Diameter Calculator
This calculator determines the blank diameter prior to thread rolling for 60° ISO metric and Unified threads.
It uses the standard basic-pitch-diameter relation PD ≈ Major − 0.6495×Pitch and then subtracts a small
setup allowance (default 0.05 mm or 0.002 in). You can change the allowance to match your
dies, material, and class of fit.
Formulas used
Metric (ISO 60°): Pitch Diameter d₂ ≈ Major − 0.6495 × Pitch.
Unified (UNC/UNF/UNEF 60°): Pitch Diameter E ≈ Major − 0.64952 ÷ TPI (since Pitch = 1/TPI in inches).
Recommended rolling blank: Blank ≈ (Max Pitch Diameter) − Allowance, with a starting allowance of 0.05 mm or 0.002 in, adjusted to suit material and die setup.
The 0.6495 constant derives from 60° thread geometry: 0.75 × tan(30°) × Pitch. For UNJ/MJ, the flank angle remains 60°, so the basic pitch-diameter relation above still applies; check the relevant standard for class-of-fit limits.