![]() ![]() In order to guarantee sufficient overlap, the finished components are generally made to form the following fits : Hlg, Hlh or GlhĮ.g., for M 6 threads, the usual fit is 6H/6g for M12 x 1.25 threads, the usual fit is 5 HI4h and for Af 20×2 threads, the usual fit is 7G/6h.ĭisposition of tolerance zones for internal threads Fie. ![]() Actually large number of tolerance classes are possible by combining various preferred tolerance grades and positions. 14.10.Ī selection of grades and positions constitutes tolerance classes. The tolerance positions for external threads are designated by letters e, g, h and for internal threads by G and H, and their disposition are shown in Fig. The various tolerance grades recommended for the crest and pitch diameters are as follows: ISO Metric threads-Design Profiles of Internal and External threads. IN PRACTICE THE ROOT IS ROUNDED AND CLEARED 8EY0NO A, WIDTH OF P/a commercial bolts and nuts) and 7,8 and 9 for threads produced by less precision methods). ![]() There are 7 tolerance grades (viz., grades 3, 4, 5, 6, 7, 8 and 9) in use, out of which 3, 4 and 5 are for precision threads, where little variation of fit is desired and where length of thread engagement is short), 6 for medium quality (e.g. The tolerances on ISO Metric screw threads are defined by tolerance grades and tolerance positions. ![]()
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