This International Standard specifies requirements for the accuracy of general-purpose hobs of 0,5 module to 40 module. These hobs are intended for producing gears which conform to ISO 53 and ISO 54. This International Standard applies to hobs for spur and helical gears. It applies to solid (monobloc) and inserted blade hobs. The elemental features of hobs are graded according to accuracy, as follows: — Grade 4A; — Grade 3A; — Grade 2A: — Grade A; — Grade B; — Grade C; — Grade D. Grade 4A is the highest order of precision. In addition to the elemental tests for hobs, this International Standard gives permitted tolerances for composite tests that are taken along the cutting edges on the line of action. The two groups of tests are not equivalent and one shall choose between one or the other. If there was no previous agreement, the hob is regarded as belonging to the precision class specified if it satisfies one or the other of the two methods of inspection. NOTE The tolerances in this International Standard were determined for gear hobs whose dimensions conform to ISO 2490, but with certain precautions they can be applied to hobs not specified in this International Standard.