Replacement Caster - 4 *Twin Wheel Casters Have Threaded Stem For Extra Security And Safety *MJM's Exclusive Reinforced Caster System Allows Additional Structural Support To Our Entire Product Line - Our Positive Engaging Lock Holds The Wheel Securely So There Is No Swivel Movement 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) *Quiet Mobility (Hard Treads Make A Lot Of Noise)*Non Rust Plastic Body And Wheels *High Load Capacity (160 lbs) *Non Slip Tread. Double The Tread Surface For Superior Breaking *Easy Reach Brake Tab