This is a set of couplers for ball-lock Corney kegs.
Two types are available: threaded and barbed. The barb type will fit any standard 1/4″ ID tubing. Simply use a hose clamp. The threaded type, though, is easier to disconnect.
Couplers are sold in sets of two as shown in the photo. You’ll get the liquid-out and the gas-in coupling.