Abstract: The window assembly comprises a main frame made up of an extruded head, sill and side members. A stationary panel is secured within the frame. A sliding panel independently framed is secured to the main head extrusion through an elongated, rigid plastic key which is secured to the top of the slider head frame member of the sliding panel. The plastic key is slidably positioned in a keyway channel extending along the main frame head extrusion so as to suspend the sliding panel therefrom as the sole means of support. Both the keyway channel and the key have downwardly sloping, mating surfaces along which the sliding panel is suspended. A portion of the key may be metal and an integral part of the slider head as long as plastic inserts are used to avoid metal to metal contact. Spaced and overlapping leg sections of the sliding panel frame and the main frame restrain the sliding panel in the main frame should the key become disengaged or broken.