works with most hubs to give the right chainline and tension..works up and down…which is nice…

The 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 singlespeed drivetrains. The Singleator features a triple-sealed spring, large cog capacity, chain guides, fully-adjustable chain line, floating pulley, and a stainless-steel pivot bushing. The main body is forged, so it’s strong. We’ve gone with an 11-tooth pulley for smooth, quiet operation. And it now works with both 1/8" (BMX) and 3/32" (geared bikes) chains. Beware impostors; the Singleator is the granddaddy and outperforms all others.

Notes: Surly Singleator comes with PUSH DOWN Spring installed and PUSH UP Spring in packaging