Surly Singleator, Black

Surly Singleator mounts right up to your derailleur hanger and provides a simple, effective, and adjustable means of tensioning the excess chain slack found in vertical dropout single-speed drivetrains.
Triple-sealed spring, large cog capacity and chain guides
Stainless steel pivot bushing
Includes two springs for upward or downward tension adjustment
Do not use with a coaster brake, fixed gear, multi-cog or multi ring drivetrains