Covers gear hobs for general purposes from 1 d.p. to 20 d.p. inclusive. It applies to three grades of ground profile hobs, AA, A and B, and two grades of unground hobs, C and D, and specifies all the dimensions for b oth single and multi-start hobs. The d.p. range is arranged in preferred sizes, together with some additional non-preferred sizes. An appendix t abulates dimensions for both the parallel and the tapered arbors for mou nting the hobs.