Upgrade your Ace to fixed gear simplicity with a Gates Carbon Drive CDX fixed sprocket! Comes in two sizes for leisurely cruising (20T) or spirited riding (19T). CNC machined from stainless steel for exceptionally long life. Fits Ace of Spades and Clubs. For Ace of Clubs, please note that a CDX front sprocket and belt are also required for fixed riding. Due to the dished profile of Gates sprockets, a deep-well, 16-notch Hollowtech style bottom bracket tool ( available here ) is necessary for lockring installation.