Intek Strength - Armor Series Competition Style Urethane Bumper Plate (Single)CPU urethane encased outer shell provides unsurpassed durability 5. 50 hard chrome steel center number with 2. 02 precision center bore One piece steel hub, no bolts or welds Urethane shell is molded and cured around a larger inner flange to ensure the strength and stability of the bumper as one unit Urethane encase has low bounce creating a safer environment for users Outer diameter measures 17. 70 for all increments Gray urethane weight increment