Measurement of Pitch Diameters of Internal Triangular Screw Thread with Large Lead Angles by Over-Ball Method

Abstract

The present paper deals with the formulas to calculate the pitch diameters or the radial measurement over one ball of the internal triangular screw thread, which have one or multi-start threads and large lead angles, in measuring internal screw threads by over-ball method. Furthermore the best measuring ball diameters which contact in the pitch diameter of internal screw thread are calculated. The approximate formula to calculate the pitch diameter of internal triangular screw thread with high accuracy without using the trial-and-error method is obtained, and the accuracy of the approximate formula is discussed.