Floor and architrave guides, door stops, canoe clips, packers and sleeve nuts — the small parts that keep a sliding door running straight and stop it over-travelling. Canoe clips are listed by head size and drill diameter, so match both before ordering. Guides are listed by overall length.
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.