For single or double windows and doors. Made of B-Flex marine plastic. Will not crack or discolor. Weather and salt spray resistant. Non-corrosive. Window grooves precisely .005" narrower than 1/4" window glass allowing positive pressure against glass at all times to seal out leaks and prevent rattling. Elevated slide at bottom of channel makes opening and closing windows and doors a breeze. Ideal for installing sliding cabinet doors. Comes in 8 foot lengths.