This is the one-way bearing for the HPI Nitro Star 21BB engine. This one-way bearing allows the recoil starter to grab the crankshaft to start the engine and spin freely in the opposite direction.
Features: Steel construction
Requires: Installing in recoil unit
Overall Length: 12mm (0.472)
Hex Width: 12mm (0.472)
Inner Diameter: 6mm (0.218)
Note: Also fits the Roto Start for the Savage.