Premium Exhaust Gasket Kit This Premium Exhaust Gasket Set includes a premium metal gasket, 2 stainless steel exhaust studs and 2 steel exhaust cap nuts. Please select Exhaust Stud diameter from drop down menu. 50cc/90cc, 2-stroke Minarelli engines typically use 6mm studs 50cc, 4-stroke QMB139 engines typically use 6mm studs 150cc, 4-stroke GY6 Stock engines typically use 6mm studs 150cc, 4-stroke GY6 Modified engines typically use 8mm studs *Please note: you should double check your stud size before ordering, the informa tion above is only a general guide