Installation Requirements: 23mm wheel shower door runners, suitable for glass doors with a thickness of 4-6mm. Upper and lower wheels are designed for glass apertures of 12-14mm. The upper wheel can be adjusted up to 8mm using stainless steel screws. The lower wheel spring automatically adjusts based on the upper wheel height.Shower Rollers Materials: 23mm sliding shower door wheels made of brass core with electroplated plastic alloy housing, offering strength and durability.Wide Use: Replacement roller runners fit most standard shower enclosures, including steam rooms. Installed at the top and bottom of the shower door for smooth opening and closing operation.Easy to Install and Use: Operates quietly with no noise when opening or closing. Ensures smooth sliding performance. Simple to install and maintain. Ideal for DIY replacement.Package Includes: Set of 4 single shower door rollers (2 top rollers + 2 bottom rollers). Each set includes 4 bumper blocks and stainless steel mounting screws.Material: Brass, Stainless Steel, Nylon.Strong Load-Bearing Capacity: Features a thick brass shaft for enhanced weight support.Ultra Quiet: Integrated ball bearings ensure silent, smooth, and stable operation.Stable Performance: Even force distribution on the upper rail allows effortless push-pull movement. Lower rail provides smooth, low-friction sliding for energy-saving and safe daily use.