This wheel hex adapter is produced for TRAXXAS TRX-4 HD applications and is listed as JR-TRX417-5MM. The component is a brass 12mm hex insert, 5mm thick, intended to interface with TRX-4 HD wheel hex hubs and typical scale crawler wheels.
Fitting is simple: the adapter slides onto a 12mm wheel hex hub and secures wheel position at the axle interface. It can be used as a replacement insert or a spare hop-up where a brass interface is desired for improved wear characteristics.
Functionally the adapter supplies a durable metal contact surface and a fixed 5mm offset that assists with small alignment or clearance corrections during wheel setup. This is an aftermarket accessory compatible with TRX-4 HD assemblies.