The square convoluted tube is used as a flexible take off from any solid ducting to equipment located in a lower rack. It fits using a square sheath to DROP OFF 50mm SQUARE ASSEMBLY (Part No. TC1279-89KIT); which slots into a cutout provided by the cut out tool (Part No. TC1279-50KIT). Each 350mm length is a snap – fit into each other to form any flexible length desired.