Slip the new rotor over the axle flange and index it to the studs with small bushings or fitting rings (arrows). These rings keep the rotor positioned on the axle, since the center lip on the axle may not fit perfectly. These rings reduce the radial runout of the rotor to an acceptable amount and must not be left off. Make sure the beveled side of the rings face the axle. Regular lug nuts are installed with the flat face to the rotor for proper rotor retention and subsequent installation of the caliper. If you're running acorn- or shank-style lug nuts on your wheels, get standard threaded ones for this step.