gearbox sprocket nut 1 1/2`` A/F

Yes it is Graham, see my reply under your original post ref Navigator tool box lid thread!

Hi Graham, it is a left hand thread, there are two left hand threads on the Navi, the other is the oil pump drive on the crankshaft.

The two left-handed threaded nuts rule applies to the all the post war Norton twins, both heavy and light. All other engine and gearbox threads are right-hand.

There are two other threads which are unusual on these Norton,s post 1960.  The badge screws are 3BA and the rocker adjuster screws are 9/32" Cycle.