Powerflex differenitial bushing inserts for your F2X, and F3X. These inserts work with the stock bushings and fill the voids in the original bushings to increase stability during hard acceleration.
Powerflex urethane differential mount inserts on the F22 2-series, F30 3-series, and F32 4-series give a more direct transfer of power within the driveline. Stock rubber mounts will twist and "wind up", especially with power upgrades. This can lead to broken bolts and mounts. Urethane bushings are stiffer and do a better job of resisting wind up.