This is a tip retainer nut that holds the Non Contact Nozzle onto the Nozzle Body, used on the Laser Mechanisms / Cincinnati cutting head.
Cincinnati # 923021
Laser Mech # PLTRA0321
Disclaimer
All products are fully compatible with referenced brands, but are not affiliated with, authorized, endorsed, or sponsored by any Original Equipment Manufacturer (OEM) or named brands, unless explicitly stated in the product description.