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 adaptor. Then both carrier and sprocket are held in place with the lockring. To change ratio, simply undo the lockring and remove the sprocket. Slide on a different tooth size and refit the lockring.
Made from chrome-plated steel and you get the sprocket and sprocket carrier.