Southwire - Topaz carries a complete line of built to last, cULus listed weatherproof electrical fittings fabricated for multiple commercial and residential applications. Our 4 in round, 4 hole extensions, companion to our round boxes expand cubic capacity while enabling a flush finish. Constructed from corrosion-resistant copper-free aluminum, UL listed for use in wet locations and complete with gaskets and mounting screws for easy installation.