This item should be replaced whenever the exhaust system is removed for service or inspection. Leaking exhaust gas is not only dangerous but it robs power from your engine. Be sure to replace this gasket when required. Gasket measures 39mm OD, 32mm ID, 4mm thick. Suits ATC90 70-78, ATC110 79-85, XL75 77-79, XR75 77-78, XL80S 80-85, XR80 79-84, XR80R 85-91, CL90 67-69, CM91 66-69, CT90 66-79, S90 84-69, SL90 ’69, ST90 73-75.