It is Strong™ Mount Adapter Plates for Converting 200mm x 200mm VESA up to 400mm x 400mm VESA. The great thing with standards is that there are so many to choose from. In order to meet the never-consistent VESA mounting patterns of displays, the Strong™ SM-ADP-M-400X400 adapter plates give you greater flexibility beyond the the mount's standard 200X200 pattern.