Technique for determining thread accuracy

A method of determining, with a hand held micrometer of the type having an anvil, a spindle, a mechanism for manuipulating the spindle relative to the anvil and means for displaying the distance between the anvil and spindle, whether the threads of a threaded member are to tolerance, the threads comprising a root, a crest and a pair of flanks connecting the root and crest and defining therebetween an acute angle, the method comprising selecting a single wire of circular cross-sectional size as a function of the number of threads per unit length of the threaded member in accordance with the relationship wherein W.times.N is substantially constant, W is the wire diameter and N is the number of threads per unit length of the threaded member;

• placing the single wire in tangential engagement with the flanks of the thread at the pitch diameter, the wire being of sufficient size to extend above the top of the thread crest;
• placing the threaded member and wire in the hand held micrometer with the anvil and spindle engaging the wire on one side and the thread crest on the other side and measuring the distance between the thread crest and the edge of the wire extending above the top of the thread crest;
• and comparing the measured distance to a calculated value M wherein M=D+0.75W-0.32475/N wherein D is the major diameter of the threaded member, W is the wire diameter and N is the number of threads per unit length of the threaded member.