Miche's unique system allows for a fast change of sprocket ratios.
A splined adaptor (not included, but available separately) 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 a lockring (again, not included, but available separately). To change the ratio, simply undo the lockring and swap the sprocket.
Made from heat treated, nickel coated steel.