Cast bronze. It is designed for easy installation and cleaning. Features include mounting lugs cast into both sides to assure universal mounting, four outside tie rods and a 304 stainless steel strainer basket to minimize electrolysis. Screen hole size diameter .077 inches, 46% open area. Hinged lugs for the cast bronze cover permit easy removal and cleaning of the strainer basket. A drain plug in the bottom casting is provided for easily removing sediment and draining for winterizing. Tested and accepted for labeling and UL listed.