This is a Replacement Kodiak Trailer dacromet coated disc brake rotor.  Kodiak part number ROTOR-12-DAC.  This brake rotor is designed to slip over 6 bolt idler hubs with a 6 on 5 1/2" bolt pattern that have 1/2" studs.  This slip on rotor goes over top of your hub, and then your tire and wheel goes on, and everything is tightened into place using the lug nuts.  The Kodiak vented brake rotor measures 12 1/8"  outside diameter.  All Kodiak rotors are 100% tested and balanced.   Kodiak on uses rotors that are vented to help dissipate heat faster.  This rotor is for use with 15" or larger wheels.  Kodiak also offers a 3 year warranty on all their dacromet coated parts.