I wasn't going to apply a pair of pliers to the knurled ring because I didn't want to wreck the knurling. But according to the patent it turns to release the blade (by an eccentric) but does not come out of the ferrule. Different blades can then be inserted. Seems like a great design. Now I know why, on ebay, there are examples of No.95 with different length blades.
So possibly the Winchester driver has a similar set-up?