This item was previously and exclusively available for the F104X1 chassis. It is now available as a standard option part for all versions of the F104 chassis. The rear shaft counterweight aids in balancing the left side of the F104 chassis without sacrificing rotational mass. The rear shaft counterweight may be used with included with F104 chassis machines that have differential components on the right side of the gear case. Installing this counterweight on the opposite side helps optimize the left/right balance and improve rear wheel traction. This freewheel weight (19.7g) is equipped with ball bearings so its effect on the axle shaft is minimal.