Gear Terminology
Diametral pitch (Pd): The number of teeth of a gear unit pitch diameter. The diametral pitch is, by definition, the number of teeth divided by the pitch diameter. That is,
Where
Pd = diametral pitch
N = number of teeth
D = pitch diameter
Pd = N/D
Module (m): Pitch diameter divided by number of teeth. The pitch diameter is usually specified in inches or millimetres; in the former case the module is the inverse of diametrical pitch.
m = D/N
Velocity ratio:-
d = Diameter of the wheel
N =Speed of the wheel
w = Angular speed
