Miche's unique system allows for a fast change of sprocket ratios. The splined adaptor screws onto the hub just like a normal cog, then simply slide the sprocket onto the carrier. Then both carrier and sprocket are held in place with the lockring. To change the ratio, simply undo the lockring and remove the sprocket. Slide on a different tooth. Sprockets and Carriers sold seperately.
Best Price: £14.99 from Leisure Lakes Bikes