Brant Twist Lock Connectors (Nema L6-20) - cleaning out the warehouse. New (old stock). Made in USA (not sure about current production). Price is per connector. Cheapest I've seen these online is $13.50ea on Amazon. Limited supply at this price.

• 2-pole, 3-wire, grounding, rated 20A 250V.
• Cord capacity: .300-.950" diameter