Surly Surly Big Dummy Frame Protective Plug Insert. - Notice the tapered end of each plug, if the end of a tube is dented, tap the protective plug into the tube with a soft hammer to round the tube out - Designed to prevent damage to the front bridge tube while frame is being shipped - Doubles as a tool to help round out any damaged bridge tubes or upright tubes during use of the bike - The diameter of the plug is designed to round it out to the correct diameter so that it receives accessories properly