This listing is for one of Gibraltar Chrome Hinged Memory Wing Lock.
From Gibraltar: "Hinged memory locks make it easy to add another drum or cymbal to your rack without taking it apart. It's simply added or removed because of the hinge. These memory locks are designed to be used at the knuckles of the rack, which means the joints. They have a male tab that fits into a female cutout that locks the bar into the same position every single time which also adds stability."
WARNING: Cancer and Reproductive Harm - https://www.P65Warnings.ca.gov