The Bolt is the most widely applied product in the XT350C 1991 (M) CALIFORNIA AIR FILTER ( four times ).
The lowest price component in this Air Filter parts-list fiche is the Bolt.
A sample from the products for the Air Filter include: Washer, Plate (517), Clamp Hose 278144550000, Joint, Carburetor, Joint, Air Cleaner 1.