Gearboxes
Module (m)
The module m is the ratio of the reference circle diameter d to the number of teeth z (m = d/z) in millimeters. It determines tooth size and is standardized in preferred values per DIN 780. Two gears can only mesh if they share the same module.
Definition and Formula
The module is derived from m = d/z, where d is the reference circle diameter and z the number of teeth. It is directly linked to the circular pitch p = π·m, the distance between two successive tooth flanks on the reference circle. Common standard modules per DIN 780 include 0.5 / 1 / 1.5 / 2 / 3 / 4 / 5 / 6 mm. The larger the module, the larger and more load-bearing the tooth — and the fewer teeth fit on the gear for a given diameter.
Example Values: Module, Tooth Count and Reference Diameter
| Module m | No. of teeth z | Ref. circle d = m·z | Circular pitch p = π·m |
|---|---|---|---|
| 1 | 20 | 20 mm | 3.14 mm |
| 2 | 20 | 40 mm | 6.28 mm |
| 3 | 20 | 60 mm | 9.42 mm |
| 5 | 20 | 100 mm | 15.71 mm |
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