Thread Checking Three Wire Method
Three Wire Method of Checking Thread Pitch and Size
The effective or pitch diameter of a screw thread may be measured very accurately by means of some form of micrometer and three wires of equal diameter. This method is extensively used in checking the accuracy of threaded plug gages and other precision screw threads. Two of the wires are placed in contact with the thread on one side and the third wire in a position diametrically opposite locations.