Parts such as the Air Cleaner: Ybs66-6 Washer, Plain, Screw Pan Head, Washer(6a1), Case, Air Cleaner 1 are included in the Rt3 1972 1973 Usa Air Cleaner parts fiche.
In this schematic the "Screw Pan Head" is used most often.
The fifteen Rt3 1972 1973 Usa Air Cleaner component parts are all listed in this schematic.