Gear Definitions, as follows;

Tooth sizes and pitch (spacing) are generally expressed in two ways (metric+imp)

DP (Diametrical Pitch)
The number of teeth per inch of Pitch Circle Diameter (PCD) - How many teeth per inch around the outside of the gear (large number=small teeth and small number=big teeth)

MOD (Module)
The Pitch Diameter (in mm) divided by the number of teeth. So a 60mm gear has 60 teeth at MOD 1, 30 teeth at MOD 2, 20 teeth at MOD 3 etc.


Hope this helps, cant advise on what size to use, cos we dont. (use chain drive)