4″ 100mm Castors. Rubber Tyres for Smooth Ride. Strong Steel Frame. Fixed- Swivel & Break OptionsSafe running load 250Kg [per4].. 4″ 100mm castor wheels with double ball race swivel on non fixed styles with steel frame and rubber tyres. There are 3 options to choose from in the range- fixed- swivel and breaked/locking.