5 or 10 slot clear linking frames that are used to join seed pixel matrix panels on the end of the rows that do not have any connections to maintain the 25mm spacing. 
Made from 1/8 inch clear acrylic which makes them unseen at night when the display is active. 
The 5 slot version is provided to use when joining multiple panels to offset the 10 slot version or if flexibility is needed within a panel to allow to flex.