Abstract: An improved window includes pivot pins at each side of the window sash. The pivot pins are received within guide channels in a window frame for mounting the window sash. The window sash may be quickly and easily mounted within the window frame by merely inserting one of the pins, and then moving the other pin into alignment with its channel. The window sash is provided with a two-part stop surface that securely retains the window sash within the window frame. No hardware is required. The window sash is formed with a ledge extending forwardly of the window sash that abuts a forward end of the window frame, and a rear corner of the window sash abuts a rear face of the window frame such that two stop surfaces are provided between the window sash and the window frame.