Main shaft gears are mainly used in the model of toy car assembly or small motor above, such as hollow cup.130.140.260.370 and other motors.

This link uploads all round hole plastic gears, need metal gears or D gears, you can search in our shop.

Examples of model descriptions are as follows.

122A gear: 12 teeth, 2A means with the diameter of 2.0MM shaft tight fit. The hole diameter is about 1.95mm.    

Gear outer diameter calculation formula: outer diameter = (number of teeth + 2) * 0.5, of which 0.5 indicates the modulus, the modulus of this gear is 0.5.