The cupped washer is the correct fitment for the Triumph pre-unit and early unit twins using the locking tab washer and main shaft clutch spigot nut. Applicable to Triumph 350, 500, and 650 models from 1955-1967.
The thick clamping washer is of a special cupped design. The washer forms an abutment for the tab washer and main shaft spigot nut within the bore of the clutch center. Made in the UK.
The mainshaft clutch spigot nut is located through the locking tab washer and cupped washer. When the desired torque specification is attained, the tab washer is bent up to lock the nut in place.