Most common installations are on a vertical wall, but our AB40 Horizontal Adapter Bracket can serve as a horizontal adapter, providing a 90-degree bridge between the wall plate and the TV mount lifting arm. This allows the wall plate to lay flat on a horizontal surface such as a large shelf or inside a recessed alcove. NOTE: The AB40 will also require the purchase of the SSB40 Single Stud Adapter to provide the correct mounting pattern if mounting an MM340 or MM540 Mount to a horizontal surface. The MM700 and MM815 mounts attach directly to the AB40 Horizontal Adapter Bracket and does not require the SSB40 adapter. NOTE: The MM750 Pro Mount is NOT meant for horizontal mounting.