These are used if you need to have two signs mounted on one pole back to back. They are only compatible with the anti-rotational D-Clip. The back-to-back clips are not compatible with the universal clips due to their set length- they work by holding on to the back sign’s rail and securing to the space on the edge of the rail left by the 'D'-clip. To mount two signs back to back you would require two Rigid 'D' clips and two sets of the back-to-back clips.