defined by a base portion 8 a first arm 9 and a second arm 10 in accordance with the invention the first arm 9 and second arm 10 of structural member 5 have end portions 11 and 12 that are turned inward the end portions extend in a direction toward the base portion 8 fastener 13 is adapted to nest on the inside surface of the end portions 11 and 12 and to slidingly engage therewith fig2 is a close up cutaway view of support member 1 that is depicted in the window frame of fig1 fig2 illustrates the configuration of structural members 5 6 and 7 wherein the three structural members are in overlying relation to one another and are configured to form a support member 1 in accordance with this invention the outside surface of arm 14 of structural member 6 is in overlying relation with at least a portion of the outside surface of the end portion 11 of structural member 5 the outside surface of arm 15 of structural member 6 is in further overlying relation with at least a portion of the outside surface of the base portion 16 of structural member 7 fig2 also.