Installation Requirements23mm wheel shower door runners, suitable for glass doors with a thickness of 4-6mm, upper and lower wheels are suitable for glass apertures of 12-14mm; the upper wheel can be adjusted by stainless steel screws to adjust the height to 8mm. The height of the lower wheel spring is automatically adjusted according to the height of the upper wheel. Shower Rollers Materials23mm sliding shower doors wheels are made of copper swing + electroplated plastic alloy, strong and durable. Widely Use for WheelsReplacement roller runner wheel are fit for most shower rooms, shower rooms and steam rooms, and are installed on the top and bottom of the shower door to make it easy to open and close. Easy to Install and UseNo noise to open the shower door and these glass door roller help it slide smoothly. It is easy to Install and Maintenance. It is easy and convenient for this door knot DIY replacement. Package IncludeSet of 4 single shower door rollers/wheels/runners/pulleys ( 2 top roller +2 bottom roller )4 x 23mm shower door rollers including 2 top rollers and 2 bottom rollers. Comes with 4 sets of bumper blocks and stainless steel screws.Material: Brass +Stainless Steel+Nylon. Strong load-bearing capacity: The coarse copper shaft has stronger load-bearing capacity. Ultra quiet: Built in smooth ball, sliding silently, stable and powerful.Stable: The force on the upper rail is uniform, and the pushing and pulling are smooth; Smooth sliding of the lower rail, labor-saving, and safe to use specifications.