Roller housings can differ even where doors look alike. Provide the door maker or part reference if known and photograph accessible identification. Do not remove a heavy panel just to obtain a measurement; safe access to the assembly must be planned first.
Dents, debris or wear in the rail can contribute to difficult movement. A roller replacement quote should distinguish these from a roller fault. Track repair can be considered separately where suitable; new wheels alone cannot promise smooth travel over a damaged running surface.
A panel can have more than one roller assembly, and the condition of each matters. Discuss whether compatible assemblies need replacing together. Replacing only an obvious damaged wheel may leave an uneven panel if the other support is worn or cannot be adjusted correctly.
Replace accessible compatible roller assemblies on an accepted panel, set the height and check ordinary travel and stops. Scope limits: Ordinary non-powered safely handled panels only. No heavy specialist lifting, glazing work, powered operators, structural changes or access-control integration.