Transmission ring nuts
Moto Guzzi V700, V7 Special, Ambassador, 850 GT, 850 GT California, Eldorado, and 850 California Police models
Rings nuts are also commonly referred to as lock nuts, spanner nuts, prong nuts, retaining nuts, and lock rings.
The four speed transmission layshaft (output shaft) and the five speed transmission clutch shaft (input shaft) share the same ring nut (MG# 93601022). This ring nut is 22 mm × 1 mm and is 7 mm tall. The same threads (22 mm × 1 mm) are used on the layshaft (output shaft) of the five speed transmissions...only in a special hex nut that is 12 mm tall (MG# 14219310).
It is rumored that the hex nut can be used in place of the ring nut.
Thanks to Tom Halchuk for sending me information on sourcing these parts.
The Whittet-Higgins Company manufactures ring nuts and special locking washers of the proper dimensions.