If your familiar with semi trucks the same things used to hold the brake chamber push rod to the slack adjuster. They see millions of cycles and are used in clutch linkage, throttle linkage and other areas. I have places where I can get a variety of sizes quickly and locally.
They are shaped like a U with the base threaded and a pin through the "forks" that you cotter key in. Just allows for quick&easy disassembly. Like you said though, and Gus, heims are more than adequate especially if you know what ones to get.
Good luck