"Even if it ain't broke, you can still fix it with our Surly Fixxer hub converter. The Fixxer allows you to convert any Shimano cassette hub (except Silent Clutch, 2004 Dura Ace or pre-1997 Dura Ace) into a true fixed-gear. By simply removing the cassette body and replacing it with our adapter, you can use a fixed track cog and lockring for safe coast-free riding. A popular conversion for track racers, spring time trainers, fixed-gear commuters and messengers, the Fixxer includes all parts necessary for installation, including axle, bearing, cones, spacers, and axle nuts. Most converted hubs can be spaced 120, 126, 130 or 135mm, and can even be used with a freewheel if a freewheeling single-speed conversion is desired."