Ansi B 92.1 Pdf 38 !exclusive! Official

| Standard | Region | Key Difference | | :--- | :--- | :--- | | | USA (Metric Module) | Uses metric modules (0.5 to 10 mm) instead of English pitch. | | DIN 5480 | Germany | Also metric, but different tooth root design. | | ISO 4156 | International | Harmonized with ANSI B92.1 for 30°, 37.5°, and 45° splines. |

The standard establishes specific tolerance classes—typically 4, 5, 6, or 7—that permit a "mix" of mating members. For example, a Class 5 internal member can be combined with a Class 7 external member to provide an overall assembly tolerance in the Class 6 range. This flexibility reduces manufacturing costs, as one member can be produced with looser tolerances if the other is held to stricter specifications, while still satisfying the overall design requirements. ansi b 92.1 pdf 38