With metallic rollers, try to be able to see exposed ball bearings, which you should grease. Nylon rollers will either have no ball bearings or sealed ball bearings. Like with plastic rollers, some companies assert it is possible to grease the nylon rollers that have no ball bearings but, https://garage-door-opener-instal08487.amoblog.com/top-preventing-common-garage-door-issues-secrets-48949923