This is a modular L-plate by Really Right Stuff, composed of a Arca-swiss compatable base plate and an L- component in order to allow switching between horizontal and vertical shooting. The L-component allows access to the battery door and all the cameras ports. The two components can be separated slightly if more room is needed for tethering or cable release. A hex wrench fits on the side (included) so that it is always handy. Sells for $185 new.