This Caster Corner, for lack of a
better term, was custom designed and built.
It is made of 1/4" steel plate & angle
iron. As you can see, it fits the 2x4 nicely. Countersink the holes and the
platform lid sits flat.
The holes in the angle plates are to screw
into the bottom of the platform's frame. A hole is drilled into the side to
allow another platform to be bolted to this one.
Here it is in action. This particular frame
is part of a tree base being built for Into the woods . The lid is being left off so a technician can be inside the tree to move it on
& off stage.See the page "TreesT, Drilling holes in the sides of the metal holds these 2x6 pieces square.