Flanged Deck Bush. A through deck bush, also known as a fairlead, is designed to protect a surface from a rubbing rope or wire, they can also be used as a deflecting point. In most applications, a through deck bush is used to guide a rope through a surface, such as the thwart or strut of a boat. It also offers protection to the material the rope or wire is passing through. Aluminium through deck bushes are available in a choice of 6 colours, allowing you to add a personalised touch.