4 Inch Kingpinless Thermoplastic Rubber Wheel Swivel Caster with Swivel Lock SCC Lastly, Service Caster’s Series KP30 casters are finely crafted with grease fittings, and 4 position notches to accept 4-position locks. When searching for a reliable and durable solution to your caster needs, consider Service Caster’s Series KP30 thermoplastic rubber on polyolefin core donut tread casters.