Discreet coloring preserves the appearance of these casters and conceals dirt. Non-marking treads keep floors looking like new. Quiet casters reduce noise pollution and roll smoothly. Designed for use with WaveBrake? mopping systems (sold separately). Caster/Glide/Wheel: Caster; Color: Dark Gray; Stem Type: Bayonet; Wheel Tread: Non-Marking.