Precision interior gears of XRAY Active Diff are die-cast and squeezed from high-grade metal product making use of high force to be sure a tremendously strong core, then are especially hardened to be sure minimal use and longest life. Includes 2 bevel gears and 4 satellite gears. Fits: #325100 XRAY XB2 Active Differential - Set #365100 XRAY XB4 Active Differential - Front/Rear - Set #365101 XRAY XB4 Active Differential - Center - Set