Grundfos 91584911 Cast Iron Pump Flange Kit is compatible with Grundfos Circulator Pumps that feature GF 53 pipe connections. This kit includes (2) flanges, (2) flange gaskets and (8) bolts and nuts. Features NPT end connections and a 2-1/2" fitting size. Constructed of durable cast iron material. Check manufacturer recommendations to ensure a proper fit.