On this parts fiche the Nut,6mm is the most specified component.
A sample from the products for the Air Cleaner/mufflers include: Muffler Assy,l.h, Holder,exhust Pipe, Holder,air Cleaner, Air Cleaner Assy.
The most reasonably priced component used on the Kz750b1 1976 Usa Canada / Mph Kph Air Cleaner/mufflers is the Nut,6mm.