Three-Wire Thread Measurement
For external, single-start 60° threads. Unified uses Classes 2A and 3A. Metric uses normal-length Classes 6g and 6h.
Wire Selection
Enter the certified measured diameter of the wires you actually use, then select Get Wire Measurements. Any change to the wire diameter clears the previous measurement result.
Calculation Basis
Scope: external, single-start Unified inch and ISO metric 60° threads only. Unified pitch-diameter limits are calculated for Classes 2A and 3A using the standard Unified tolerance formula and standard length-of-engagement basis. Metric pitch-diameter limits are calculated for normal-length Classes 6g and 6h using ISO 965 product-limit data. The implementation preserves the published whole-micrometre tolerance values rather than reconstructing table values from unrounded formulas.
Best wire size is 0.57735 × pitch. The practical wire range used here is 0.56 × pitch through 0.90 × pitch. Measurement over wires uses the National Bureau of Standards / NIST lead-angle-compensated three-wire method rather than the simpler zero-lead-angle approximation. The Unified thread and three-wire basis uses NBS Handbook H28 as the primary public technical source. Metric tolerance limits use the ISO 965 tolerance system with independent product-limit cross-checks.
The actual calibrated wire diameter is used in the measurement calculation. This tool does not substitute for calibrated wires, controlled measuring force, or the applicable inspection/gaging specification.