1.This item replaces 5379X; please check your original manual to verify your model uses the 5379X gear set. 3.It is know to fit the E/MAX front/rear diffs, the E-Revo front/rear diffs, the Rally VXL front diff, the Revo 3.3 front/rear diffs, the Slash 4X4 front diff, the Slayer Pro 4X4 front/rear diffs, the Summit 4X4 front/rear diffs, the Telurid4X4 front diff, the T/MAXX 3.3 front/rear diffs, and the XO-1 front diff. 4.The surface of this gear has harden coating.The origial is only ordinary pot black. 5.The material is chrome steel.Hardness is HRC52.