This is the retaining ring that secures the wire arm that holds the pump in place. Also known as a push nut. this ring is also used on the Dragonfly stove to attach the burner cup assembly onto the 'enclosure'.
Not shown on the diagrams, but it is part of part number 419220 Catch Arm Assembly, and part of part number 419832 DF Legs & Enclosure Kit.
Part Number: 419154.