Shimano Dura Ace NJS Racing Track Bike Cog

This is the NJS approved, track racing fixed cog from Shimano Japan.
It bears the Dura Ace name, and therefore represents the finest in Japanese production.
16T is generally better for street use, 14 and 15 are very popular in pro keirin racing.
13T is to be used for the track with lighter chainring sizes, or with very small bmx front chainrings for trick/track bikes.
Shimano cogs are designed purely for pro track racing, so they never made anything above a 16T cog.
Please check out the Euro Asia Import cogs, if you are looking for something larger than a 16T.