Rollers, carriages and nylon guides for sliding wardrobe, robe and cupboard doors. Top-hung and bottom-rolling types, sized to the track. Nylon guides are listed by overall length so you can match the one you removed. Lighter duty than patio door hardware — check the load rating if the door is solid rather than a framed panel.
Not sure which one? See the Sliding Door Roller & Carriage Buying Guide, look up a part number in the roller part number finder, or browse all rollers and carriages.