The TS129 Progressive Clip is pre-attached to the top frame of a panel and provides the means of a screw attachment to the substrate.  It also provides a socket to receive and carry the next panel above and automatically fixes the joint witdth of 1/2".  If a 3/8" joint is required, the extrusion is set back 1/16" from the top and bottom panel edges which closes the gap between panels to 3/8".   This allows the installer to work progressively upward instead of installing all the horizontal runners then the panels.  The TS129 is compatible with TS138 and TS140.