Problem Solvers Chain Tensioner and Derailleur HangerThis little device will stop your rear wheel moving forward when you stomp on the pedals. It will also give you a derailleur hanger to bolt a derailleur onto. That makes it very useful for converting track frames into geared city bikes. Will take either a 10mm solid axle, or a quick release skewer. For frames with track ends (also called rearward facing horizontal dropouts).