High-Quality Material: The U-groove steel caster is made of high-quality galvanized steel, which is strong, durable, waterproof, and corrosion-proof. Dimensions: The diameter of the wheel is 50mm, the inner width of the wheel is 22mm, and the outer width is 28mm. Install the 19mm round test tube rail (please confirm the size of the test tube rail before ordering). Load capacity: U-grooved steel swivel castor with a 3 mm thick bracket. Each U-groove door wheel can support up to 300kg, easy to transport Roller bearings: Dual roller bearings make sliding smooth and easy to slide into the door Wide range of applications: inverted rails, industrial machinery, rolling doors, sliding doors, factory doors, entrance doors, dog doors, container frames