Gloss Black Finish. That’s the original factory grease showing in the picture. Really, the catalyst Uniglide cog for building a Uniglide cassette. Makes a great last cog after the more common 13T to 23T cassettes. Can also be used to bridge between the 23T and 34T cogs. This is a true 600 EX cog pulled new from the Shimano factory 10 packs. Do not confuse with the lower level Exage black cogs. This black finish is higher quality. Likely, the last stash in existence. Once gone, they’re gone forever.
Fits Z-series, Exage, 105, 600 EX, and Ultegra Uniglide cassette bodies.
Also compatible with Dura Ace, except for the two smallest positions. Who would use this is anything but the largest three positions anyways?