This is a Craftsman style frame with tapered sides. The bottom rail is thicker than the top rail to enhance the tapered appearance. Each corner is fastened together using tenon joinery and then there is a choice of the type of corner treatment you want. Pictured here are pillowed square oak pegs which go through the frame to secure each corner.
The frame pictured is constructed of quarter sawn oak, finished in Mission Medium. The sides are tapered from the bottom at 2" to 1.5" at the top. The bottom rail is 2" wide and the top rail is 1.5" in width.