The Kyosho OT-19 parts bag contains the drive washers or hexes that connect the wheel axles to the wheels.
OT-19 uses a tapered hole and friction-fits to the wheels. It requires you to tighten the wheelnut sufficiently to ensure the hex doesn’t slip.
Alternatives
The OT-231 wheel hubs with screw-in pins are the replacement hex when you use the OT-229 (front) or OT-230 (rear) wheel shafts, or the LA-303 or LA-232 universals
