Abstract: The invention relates to a corner key reinforcement brace for strengthening the joint between the beveled ends of abutting tubular metal members such as found in the frame of metallic storm or screen doors. The corner key is internally slip-fitted within each of the adjacent, abutting frame members in a manner so that a relatively close tolerance is maintained between the inner walls of both tubular members and the corner key. The corner key is formed of two substantially identical half sections having first and second leg portions disposed at substantially right angles to one another. All of the leg portions are substantially U-shaped in transverse cross section with one pair of corresponding legs having the top edges of the sidewalls thereof bent inwardly.