Surly Single Speed Cog Single And Ready To Mingle Surly's BMX / Singlespeed cogs fit the (common) splines of Shimano/SRAM and Shimano-compatible freehub bodies - that's virtually every MTB hub on the market today. Built of practically indestructible hardened Chromoly steel, these cogs are ready to lick up what you dish out. Larger sizes include drillings to save weight. Incredibly durable SCM-415 hardened Chromoly steel Designed for use with 3/32" (i. e. , 8/9/10 speed) chains | Surly | Single Speed Cog 19T, 3/32" Chain