1、 Thread size out of tolerance: large pitch diameter and outer diameter / large blank diameter; Large pitch diameter, small outer diameter / the top of the thread rolling gear is not high enough, the thread rolling wheel is not pressed in enough or the tooth root is too shallow; Pitch diameter pair, large outer diameter / too deep root of hobbing gear; Pitch diameter pair, small outer diameter / small billet diameter or insufficient tooth top height; Small pitch diameter, large outer diameter / too small extrusion or too deep tooth root; Small pitch diameter, small outer diameter / billet diameter or too deep tooth root; Small pitch diameter and small diameter / small billet diameter.

2、 Position of tolerance zone: the position of the thread tolerance zone is determined by the basic deviation. The deviation es on the external thread and the deviation EI of the internal thread are the basic deviation. Two positions g and H are specified for the internal thread and four positions E / F / g and H are specified for the external thread. H. The basic deviation of H is zero, the basic deviation of G is positive, and the basic deviation of E, F and G is negative. The size of the tolerance zone is determined by the tolerance value and is divided into several levels according to its level.