Day collar or eternity collar?
One question settles it: does it ever come off?
A day collar is worn during the day, around other people, and comes off whenever you want. An eternity collar is meant to stay on, with a closure that needs a tool.
So the difference isn't how it looks or what it costs, but how it closes. A wide collar can be a day collar, and a slim ring can be an eternity collar.
Want something that doesn't read as a collar in company? Then it doesn't have to be a collar. The Ring of O says the same thing more quietly, the ear studs are a collar in miniature, and the Love Heart Necklace is for every day, when a collar would stand out too much.
Unlike a choker or chain from the high street, every piece here is made to a single measurement. That's the first thing you notice: it either fits, or it doesn't.
Still unsure? Start with the measurement. For both, that's what decides whether the piece fits as it should.