What is this? Door rollers are competitive with all track systems using 20mm diameter rollers. They can be installed on shower doors and in header rail tracks. You can also use them to replace rollers in kitchen drawers or stove drawers. You have many options for using them.What will I get?Size: Roller wheel diameter:20mm(0.79inch) Roller wheel thickness: 5.5mm(0.22inch)In the package of: Pack of 4 Shower Door Rollers with 4 screwsMaterial: Nylon, Bearing Steel, BrassColor: WhiteScrew Size: Diameter: M6, Length: 12mm(0.47inch)Brass Step Diameter: 11mm(0.43inch) Brass Step Height: 5mm(0.2inch)Is there any advantages of the product? 1. Shower door rollers have built-in ball bearings for ease of use and control. You can control the door to move in the direction you want, very quietly and without disturbing noise.