The fabled Gold Medal Pro track cog--12T to 18T. In 1/8 only. 12T comes with the required stepped lockring. For professional track racers. Perfect threads, roundness, concentricity, and tooth profiles. Titanium Nitride coating increases lubricity and durability. Ridden by the most dominant track team in the world. With wins in the recent World Championships plus the Beijing and London Olympics, this cog is appropriately named.