This gear replaces the three drive gears in a Bachmann G scale train.  Parts G811X-0ZN01; G811X-0ZN02; G811X-0ZN03   Made of durable, low friction Nylon.  It is design to work best with our Gear G811X-0ZN02 and Gear G811X-0ZN03 combination.  Buying the full set is a $10 savings.  For two shay models, please replace both sets at the same time to ensure the gearing is correct.