CasterHQ's 'LD' Series swivel casters with Gray Iron Semi-Steel wheels feature a heat treated ball bearing raceway and a bright zinc plated finish. These casters are ideal for light and medium duty material handling, carts, equipment, and shop projects. Semi Steel wheels are great for smooth, clean, concrete floors as long as there are no debris. These wheels are extremely easy to roll due to the hard durometer of the steel wheel and the friction co-efficiency when combing this on concrete floors. Semi-Steel wheels have a high resistance to impact damage while providing easy maneuverability for floors in commercial and industrial settings. These easy rolling wheels are quieter than comparable steel wheels. Semi-Steel resin wheels feature a resistance to water, oil, and grease.