I believe it is the very earliest sets of U.S Embossing Company Color Cubes that were made with with a raised edge for the diagonals, as is the case on these, dating to 1930s I am pretty sure. A nice large set of 49, these have seen a lot of use, with paint loss to some of the of the solid colored sides and only the lid of the box still around, well taped around the edges. Still great for many hours of design fun though, and display, too, with the underside of the lid features many possible arrangements for inspiration! I believe one can never have too many of these.
Cubes measure about 1 1/8" square; box about 7 7/8" x 7 7/8" x 1 3/8"