This is a good example of the rear sprocket/hub that was fitted to all SOHC Nortons with rigid frames. It should be noted that this type of rear sprocket was also used with rigid framed Sidevalve and Overhead Valve bikes postwar, and was also used later on again with the swinging arm models (i.e. pre-full width hubs, which came along in the late 1950's). As can be seen in the photo, they are packed in protective grease
For those that have previously asked, the studs are 7/16" x 26tpi and the sprocket is to take a 5/8" x 1/4" chain, as per the original.
Note: the plunger type hub is different, identifiable by having six holes - we sell this as well, Item No 0296b