Sometimes you need a smaller cog, and sometimes you need a bigger one; luckily, the Surly Single Cog caters to your fancy. The machined SCM415 Cro-Moly steel cog features a tall tooth profile to prevent chain skip and works with six-to-nine-speed 3/32in chains. Available in every increment from 13-22T for perfect gearing, the cog is stackable and derailleur compatible for multi-speed drivetrains. The CroMoly steel is heat-treated for ultimate strength properties and chrome-plated for surface hardening and improved chain lubricity.