In this schematic the "Nut,cap,8mm,black" is used most often.
The lowest price component in this Mufflers parts-list fiche is the Washer-spring,10mm.
A sample from the products for the Mufflers include: Pipe-exhaust,#2,black, Holder-exhaust Pipe,b, Pipe-exhaust #3 Bla, Washer-spring.