Not compatible with TRX4M stock chaissis as the lay lown servo mount is wider than stock. Not compatible with original TRX4M size dogbone shafts as the axle housings are 4mm extended per side. Compatible with both INJORA and stock TRX4M upgrade parts: gears, C hubs, steering knuckles, chassis links, drive shafts. Compatible with INJORA INJS2065 INJS11 servos, TRX4M stock servo. Specifications: Housing Material: Aluminum C Hubs Material: Aluminum Steering Knuckles Material: Brass Gear Material: 20CrMo Alloy Steel CVD Shaft Material: Hardened Steel Gear Ratio: 24/12=2:1 (Same as Stock) Total Length: 122mm Front Axle Weight: 106g Rear Axle Weight: 42g