Replacement hardware to suit AMP™ sliding patio doors and windows runs to five parts: four adjustable carriage and roller units and one keyed window catch and spring. Three of the carriages take a 36mm roller and differ only in load rating and roller material, at 25kg, 35kg with a brass roller and a 40kg premium version, with a further 35kg heavy duty unit alongside them. That concentration tells you what fails. A patio door that drags, jumps the track or sits out of square is nearly always the carriage rather than the track itself, and the catch spring is the other common fault on the same joinery. Measure the roller diameter and the carriage body before ordering, then match the load rating to the door, because a heavily glazed panel on a 25kg carriage will flatten the roller again.