The domed “acorn” nut is important as it is used to secure the outer gearbox cover and the primary chaincase cover. The chrome finish lends a nice look to a visually prominent fastener on both covers.
The domed nut is a chrome finished nut with 5/16″-26 TPI CEI threads, as used on pre-1969 Triumph unit-construction 650 primary and outer gearbox covers. Made in the UK.
The nut is tightened onto retaining studs with a washer under the head of the nut. Sold in pairs.