The Rohloff Speedhub Sprocket is for use with the Rohloff Speed Hub. This genuine Rohloff part allows you to perfectly match your sprocket/chainring ratio to your needs. The 15, 16 and 17 tooth sprockets are reversible, and therefore can be used from both drive sides. The 13 Tooth is for use with the Rohloff Speed Hub on small wheeled bicycles (eg 20”, folding bikes and recumbants). It uses a different chain line (58mm instead of 54mm) and is not reversible. For sprocket removal, a special Rohloff sprocket tool is needed.