Welcome to our shop The Shower Door Rollers are made of copper + POM wheel, and the track is made of stainless steel, ensuring corrosion resistance, rust-proofing, and good overall performance. These Shower Door Rollers have a strong bearing capacity and excellent stability. They have a small friction coefficient, resulting in a smooth and quiet sliding experience. Installation is easy and these rollers are commonly used for bathroom glass sliding door pulleys and rails. The roller wheel has a diameter of 23mm and comes with screws. It is suitable for shower doors that are 4-6mm thick. The inner hole of the roller wheel is 4mm and is fixed with M4 screws. The thickness of the roller wheel is 5.8mm. Package includes 4pcs of Shower Door Rollers Runners Wheels. Note: 1. Please allow small size error due to manual measurement. Thanks for your understanding. 2. Monitors are not calibrated same, item color displayed in photos may be showing slightly different from the real object. Please take the real one as standard. (Customer satisfaction is our top priority. If you find any product problems after receiving the goods, such as damage or incorrect quantity, please contact us immediately. We will try our best to provide you with satisfactory after sales service) Thank you for meeting me.I hope this helps you. Wish you a happy life.