Factory Lubricated and Sealed Roller Bearings Provides Maintenance Free Operation For The Life Of The Truck Assembly (9 Ball Type Bearings Rated@1500RPM) One Piece Steel Body Truck Assembly, Completely Enclosed In Track Assures Easy, Smooth Sliding Performance Steel Side Roller Bearings Provide Free Lateral Movement Control From Inside The Track Fits 2 1/8" X 2 1/8" ID Track. Titan Eight Wheel Slide Gate Trolley Cast Galv Steel Body Heat Treated Sealed Bearings Adjustable 4-Way Mount 10 Wheel Truck Assembly (6000 lb. capacity) Horizontal Wheel O.D. 2.125 Vertical Wheel O.D. 2.045