Standard OE replacement cog for Shimano CS-7800, 7900, 6700 11-21, 11-23, and 6600 11-23 cassette. Inside edge is knurled to grip on the lockring. Treated steel is incredibly durable.
Please note: only works on CS-7800, 7900, 6700 11-21, 11-23 and CS-6600 11-23 cassettes. This cog can't be used to retrofit a cassette with a 12t or 13 small cog.