Micro Traders 4X Zinc Alloy Top& Bottom Shower Door Twin Wheels Rollers Runner... Set of 4 Twin Shower Door Rollers (2pcs top and 2pcs bottom) Suitable for most shower enclosures, shower cabins and steam cabin enclosures Materials: 304 stainless steel micro-bearing POM zinc alloy brass axis Wheels diameter: approx. 23mm / Glass door thickness: 6mm They are adjustable 8mm up and down to allow the door to be lined up to mate with the frame or magnetic seal