What are OPERATING COUPLERS
If you’re talking about knuckle couplers, one in particular comes to mind; Kadees. There are copies, but after having to replace ALL of them, I’m sticking with the Kadees. The knuckle on these couplers open and close to uncouple and couple, more or less like the prototype.
The small spring on the side of the coupler keeps the knuckle closed. The curved piece under the coupler relies on magnets (permanent or electromagnets) to open the knuckle for uncoupling.
Kadees are the original operating coupler (as picture above). All others are copies and most are made of plastic, (the KD is a superior all-metal design).
Non-operating couplers are refered to as “dummy” couplers and are often used for strings of cars that are intended to be semi-permanently coupled together, such as a string of ore cars., saving the cost of the operating couplers.