4x Twin/double Zinc Alloy Shower Door Rollers for sliding shower doorsThe minimum hole size is 8mm (fits glass hole of 6mm if plastic sleeve removed).They are adjustable up and down to allow the door to be lined up to mate with the frame or magnetic seal where you have a pair of doors.Swivel action to also fit curved and quadrant showers. Diameter of wheels:23mm or 25mm (please select from the drop down menu)Width of wheels: 6mmMaterials: 304 stainless steel micro-bearing POM zinc alloy brass axis - never rustyou may receive white or black wheels depending on current stockWorkbench Casters Kit Heavy Duty Retractable Casters Side Mounted Adjustable Table Stepdown Casters