The larger diameter end is designed to fit the ID if your tailpipe. In my case, 1-7/8 for a 2" OD pipe. They get inserted thin side first into the end of the tail pipe all the way to the larger diameter is flush or slightly recessed into the tail pipe. A hole is drilled in the tailpipe to allow the nut & bolt to hold it in place. I then installed a chrome tip to extend the looks. For me, X2