1. It has sealed 6200ZZ ball bearings. 2. It is suitable for residential and commercial doors and fits 2 - inch tracks. 3. The load - bearing capacity of a single roller is about 150 pounds after 100,000 cycles. 4. The nylon material can help reduce noise. 5. It is relatively durable. 6. There is a nylon shell around the wheel, which allows it to run quietly. 7. Specification parameters: - Wheel thickness: approximately 0.48 inches - Wheel diameter: about 1.8 inches - Length: around 4.78 inches - Shaft length: about 4.25 inches - Shaft diameter: approximately 0.43 inches - Color: Black - Material: Nylon + Metal 8. Package contents: - 12 garage door rollers - Only the above - mentioned package contents are included, and other items are not included. 9. Attention: Light and different displays may cause the color of the item to vary slightly from the actual object. The measurement tolerance is about +/- 1 - 3 cm.