A single carriage suits Prongers™ patio doors: a 25kg stainless steel adjustable patio door carriage and roller, which also replaces Lidco® rollers. One part, and it is the one that fails — on a glazed sliding panel the carriage carries the full weight, so the wheel flattens, the bearing binds and the height adjuster seizes long before anything happens to the frame. A door that has turned heavy, noisy or is catching on the sill is almost always telling you the rollers have gone. Before ordering, lift the panel out, measure the old carriage body and wheel against it, and confirm the panel weight is within the 25kg rating. Stainless steel is worth noting if the door is coastal or in a wet area — check whether the original carriage is a plated one that has since rusted.