Gear hobs - Accuracy requirements

ISO 4468:2020

ISO 4468:2020


This document 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 document 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 document 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 can 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 document 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 document.


This document was prepared by Technical Committee ISO/TC 60, Gears, Subcommittee SC 1, Nomenclature and wormgearing. This third edition cancels and replaces the second edition (ISO 4468:2009), which has been technically revised. It also incorporates the Technical Corrigendum ISO 4468:2009/Cor 1:2009.

The main changes compared to the previous edition are as follows: - oversize tolerances: when the hob outside diameter exceeds the recommended size given in ISO 2490, the standard tolerances shall be increased by a factor of one-half of the percent oversize; - hob sizes: the standard hob sizes from ISO 2490 were added as Annex A.

Any feedback or questions on this document should be directed to the user’s national standards body. A complete listing of these bodies can be found at