What is it for?
A gear is a rotating circular machine part having cut teeth or, in the case of a cogwheel or gearwheel, inserted teeth, which mesh with another toothed part to transmit torque and speed.
 
Specs:
Material: Metal
A = 28 mm O.D.
B = 18 mm
C = 12 mm I.D.
D = 12.5 mm
E = 15 mm
F = M5 – 0.8