Nylon rollers provide premium benefits to standard rollers on quietness and strength.  The weight rating for sealed nylon rollers is 100+ pounds per roller with 50,000 life cycles. Overall Length: 4-5/8” Shaft Length: 4-1/8” Shoulder Width: ½” Shaft Diameter: 7/16” Wheel Thickness: ½” Wheel Diameter: 1-13/16” Fits Residential Standard 2” Track 13 ball bearing rating: 125lbs per roller @ 50,000 to 75,000 cycles Roller has a lubrication groove to disperse lubrication over a long period of time Nylon for ultra quiet operation Sealed bearings for zero maintenance 13 Balls for more durability Nylon shells around steel wheels for the ultimate combination of quiet and durability