These double-winged flush window retainer clips from Prime-Line products are constructed from stamped steel and come in a rust-resistant, zinc-plated finish. They are designed to mount on narrow, vertical rails on the exterior side of dividing window mullions to secure two adjacent window screens. These flush-locking double-winged screen clips feature a simple mounting design where only one fastener is required per clip, to hold two window screens. These types of clips are most commonly used with wood-framed window screens and include fastening screws for quick and easy installation. Removal of window screens is easy with these double-winged retainer clips. A simple 1/4 turn of the clip (to the left or right), will align it with the vertical rail to which it is fastened, freeing in this manner the screens it is holding in place.