I have heard them called “quick links”, “chain connectors”, “link connectors”. Mostly “Quick Links”. That’s what I call them and then you tell a coworker you need them they usually give you “that look” then I say, “You know, link connectors? Chain connectors? Those weird things that look like a chain link but you can unscrew that barrel so you can run it through a chain link to attach chains together or add hardware?” Then I get the half smile and the head nod and the “Oh yeah…” that kind of trails off like they have no idea but hope I will go find something else to do…like find the quick links we need.