The Zeebar stiffeners are an important part of the T.D.C. system and they are machine formed by the triplex machine mentioned earlier. The Zeebars are fastened to duct section using our new autolock machine, pictured above. The autolock machine uses a new fastening method called the Buttonlock and has eliminated many of the problems associated with stiffeners. Buttonlock uses no mechanical fasteners and the fastening procedure is acheived by use of a non-penetrating expansion punch system that fastens the stiffener to the duct without penetration of internal duct surfaces. This new fastening method provides both high strength and no leaks. Buttonlock was tested at various negative and positive static pressures and test results state no Buttonlock failed or leaked.