An addendum to my earlier post. The driver boss (with the Rogers conversion kit) slides onto the axle and is held there by a large nut that also serves to wedge it onto the tapered flats of the axle. The boss itself is threaded to recieve either the fixed sprocket or a freewheel depending on the trike's drive setup. I would expect that a lock nut would be needed for a fixed gear trike as with a fixed gear bike. I never tried such a thing with my trike; cornering is hard enough with a freewheel.