Leonard Rubin, Oct 97:
Certain Shimano cassette cogs can easily be modified to fit a Sturmey Archer hub, by simply grinding off three of the six little splines, and lightly dressing the remaining three (I've been doing this for over a decade!), yielding a wide range of lightweight replacement cogs.)
http://stein.dommel.be/brompton/ers/Sprocket.html#257

Does anyone know whether one should use a "first sprocket" with built in spacer or a "middle sprocket" without spacer for this hack?