Optimum diameter of three wires based on screw threads-basic profile and parameter definitions

Different type of screw thread measurement needs different method.In this paper,the calculation method and precondition of optimum diameter for screw thread measurement were demonstrated.According to the design principle and measurement method of screw thread,the influences of screw threads-basic profile and screw thread parameters definition to the calculation of optimum diameter of three wires were discussed.Through geometric analysis and theoretical derivation,the calculation method of the screw thread pitch diameter and optimum diameter of the three wires was further confirmed.Accurate optimum diameter can reduce the measurement error of screw thread pitch diameter,and it can theoretically avoid measurement error introduced by screw thread angle deviation.