Our Positive Engaging Lock Holds The Wheel Securely So There Is No Rotation When Locked. The Unique Design Allows Easy Movement On Hard Surfaces And Helps Eliminate The Wheel From Falling Into Cracks. Soft Non Marking Tread. (It Will Not Leave Black Marks, Or Leave Groves In Wood Or Vinyl). Quite Mobility. Non Rust Plastic Body And Wheels. High Load Capacity (160 Pounds). Non Slip Tread. Double The Tread Surface For Superior Breaking. Easy Reach Brake Tab.