I bought this old cast iron T-wrench at a Pennsylvania flea market some time ago.
It is 6 1/2 inches high, and the top of  the T is 8 inches long.  There is a large "C D" monogram as the picture shows. The larger square opening, with its bolt-end accommodation, is 13/16 inches. The smaller square opening is 7/16 inches. The open hex end is 3/4 inch.  The wrench, though cast, was provided with central ribs on both sides.

I cannot find out who made this wrench, or what its application was.  Does anyone know?

Looks to me like a sort of bed spanner or key - used to assemble and adjust wooden or cast iron beds, and the meshing mattress support (usually attached to a wooden frame, and tensioned by nuts at the head and footof the bed).