Master Flow Drive Cleats and S Cleats are used to join sections of rectangular duct and stack duct in. HVAC systems. These cleats are sleeves of galvanize steel that help to securely assemble the top and bottom S and left and right sides Drive of rectangular duct runs. S cleats are used to connect the long side of the duct, while Drive cleats are used to connect the short side.Galvanized steel constructionAlways seal seams with code approved mastic or sealant or duct tapeAlways insulate ductwork for greater system efficiency and comfortS Cleats secure bare edges of rectangular ductInsulate ductwork to promote system efficiency