Intek Armor Series Urethane Bumper PlatesCPU urethane encased outer shell provides unsurpassed durability 5. 50 hardened chrome steel center hub with 2. 02 center bore One piece steel hub, no bolts or welds Urethane shell is molded and cured around a large inner flange to ensure strength and stability of the bumper as one unit Urethane encasing has low bounce creating a safer environment for athletes Outer diameters measure 17. 70 for all increments Gray urethane weight increment markings