A friction stay top hung 300mm A023A Coastal is a type of window hardware that is used to support the opening and closing of a window. It is a type of hinge that is typically mounted at the side of the window frame and allows the window to be opened and closed smoothly and easily. The A023A Coastal designation indicates that this friction stay is specifically designed for use in coastal environments, where it may be exposed to saltwater and other corrosive elements. It is typically used in conjunction with a top-hung window, which is a type of window that is mounted on a track and can be opened and closed by sliding it horizontally. The 300mm measurement refers to the length of the friction stay, which may be necessary to ensure that it is the correct size for the window it is being used on.