Surly's Dummy Rail Collars are nothing more than a simple clamping device that buttresses the connection between your Big Dummy Frame and the Dummy Rails. They increase the stiffness of the interface of these two parts and help keep your cargo from getting its salad tossed... unless of course your Dummy Bags are filled with tossed salad. These are designed specifically for use with the Big Dummy frame and Dummy rails, and will not work with Xtracycle rails. WARNING: Properly installed Dummy Rail Collars are required for carrying live cargo on your Big Dummy.