To suit Centor™ top-hung sliding doors TradeBase lists one part, a 29mm sliding door trolley with an acetal roller — adjustable, steel bodied, and also a replacement for Trak™ rollers. On a top-hung door the trolley does all the work, which is why it is the only part here: the acetal wheel wears, the trolley picks up dust from the track, and the door begins to bind, drop at one end or run unevenly. The 29mm figure is the identifying dimension for the trolley, so pull the old one out of the track and measure it before ordering — top-hung trolleys look alike across systems, but wheel size and body width are what decide fitment. Check that the original is adjustable, since a fixed trolley of the same size gives you no height correction.