Possess Sealed 6200ZZ Ball Bearing Fits residential and commercial doors comes in 2 inch track Rate of one roller is 150 lbs at the rate of 100,000 cycles Nylon lessens the noise Highly durable The nylon shells around wheels provide smooth and quiet operation Specifications: Wheel Thickness: 0.48 inch Wheel Diameter: 1.8 inch Length: 4.78 inch Stem Shaft Length: 4.25 inch Shaft Diameter: 0.43 inch colour:Black Material:Nylon + metal Package Contents: 12 x Garage Door Roller Only the above package content, other products are not included. Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.