For Arrow™ sliding doors there are two parts: a 25mm convex acetal roller on a threaded stud rated to 15kg, and a plastic floor and architrave guide kit, the latter also listed against Manhattan™ guides. Between them they cover the top and bottom of the same problem. The roller carries the door and wears at the convex face where it sits in the track, so the door begins to scuff and run heavy. The floor guide is plastic and is what snaps or wears oval, letting the bottom of the door swing out of line. Measure the roller across the wheel at 25mm and check the threaded stud, because a convex wheel only suits a rounded track profile and a flat or V-groove track needs a different roller. Confirm the leaf weight sits within 15kg before ordering.