The GPM DSAV1639T2T Delrin 2-Speed Second Gear is specified for the HPI Savage 21 with a 39T profile to ensure repeatable shift points and controlled meshing under load. Using Delrin material provides a balance of toughness and low friction, reducing wear on mating gears and supporting consistent performance across varied running conditions. This component is intended as a straight replacement to improve longevity without changing gear ratios.