These aluminum gearbox joint option parts come standard in the Tamiya TT-02 Type SRX chassis kit. They can be used as replacement parts for that kit, or you may use them on item 22049 XV-02/TT-02 Oil Gear Differential Unit to replace the steel cups with an aluminum version. By using the aluminum cups, rotating mass is reduced thereby improving acceleration. - TT-02 Type-SRX Aluminum Gearbox Joints x2 - TRF417 V5 Swing Shaft Cap (Item 51536) x1 (Note: Replace periodically.) - Durable aluminum gearbox joints with low friction anodized surfaces give drivetrain lightness and smooth performance. - Use with swing shaft caps to limit wear on joint cups and drive shafts. - Compatible with the TT-02 Type-SRX chassis and chassis with Item 22049 XV-02/TT-02 Oil Gear Differential Unit. - NOTE: This product is intended for race cars and may be damaged by heavy duty use.