A self-leveling structural element in a non-progressive attachment system, a U-shaped retentive clip having a base and two upwardly extending arms that are forced apart by the installation of a self-drilling screw, the novel retentive clip with screw coacting with an extruded frame to mount and retain a plurality of aluminum composite material (ACM) panels in a coplanar manner, to form an Aluminum Composite Cladding System, for a non-progressive system that enables removal of individual panels for replacement or repair.