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Threaded Driver
Older Sturmey-Archer hubs used threaded sprockets, similar to track sprockets, which screwed onto a threaded driver. Sometime in the 1940's, three-splined sprockets and drivers were introduced, which made it much easier to interchange sprockets.
To remove the sprocket from a threaded driver, the driver must be removed from the hub (otherwise it will just freewheel as you turn it counterclockwise.) As shown in the photo, one good way to secure it is to set it so that the legs are straddling a suitable steel bar, held in a vise. I use a pair of headset wrenches side-by-side, then unscrew the sprocket with a chain whip.
Threaded drivers are fairly rare, and are often sought after because they have the same thread as a standard freewheel hub. This makes it possible to create a hybrid gearing system by screwing a normal freewheel onto the driver. More details on this may be found in my article on my O.T.B. 63-speed bicycle.
