Bronze 3-Pc

The roll is also perforated

They're used for controlling the volume of water flow and starting and stopping flow during maintenance and repairs

the hook is made of type-304

Cross Reference: Keeprite refrigeration fan motor

Parker Check Valve, 1/2 in, Single, Inline Poppet, 316 Stainless Steel, FNPT x FNPT - 8F-C8L-1-SS Bowl Color-Beige Bronze 3-PcInstrumentation Check Valves, C Series, 6000 psi at 115F Cracking pressure: 1 psi Max. temp.: 400F,Designed for unidirectional flow control. Custom molded seat helps prevent blowouts. Fluorocarbon back stopped poppet reduces spring stress. Valves offer heat code traceability for material certification. FNPT connections.