This is a UFP Boat Trailer replacement integral zinc plated 5 bolt hub and rotor. This is UFP part #41019 DB-35 Model. The rotor is 9.75" in diameter. The hub and rotor are machined as one piece. This hub and rotor combo are designed to fit on 3,500lb capacity axles and uses a 5 on 4 ½” bolt pattern. This zinc plated hub/rotor will resist rust in salt water environments. The studs are a ½-20 thread. The rotor is vented to help dissipate heat faster than a solid rotor. UFP disc brake hub and rotor combination uses a 1 1/16” outer bearing (44649), a 1 3/8” inner bearing (68149) and a 1.68" (inner diameter) x 2.56" (outer diameter) grease seal. This rotor will ONLY fit on UFP (Unique Functional Products) brake sets.