The white pinion gears with the 1.9 mm dia. hole are a press fit on to the 2.0mm diameter electric motor shaft.
Only the brass pinion gears listed should be used with the Faulhaber motors (Code: SMFAU). Plastic pinion gears are press-fit and are not recommended to use Faulhaber motors due to the risk of damage to the motor.
Gears are available in packs of 10 (Code: GEAR12/1.9-10) and packs of 50 (Code: GEAR12/1.9-50).