Am assuming Pete that you're saying these came loose in a box lot of various things?
They aren't of a shape that immediately says 'custard cup', but they may well be. Since their beginnings in the early C19, custard cups traditionally had a rudimentary stem of sorts and separate foot, usually, (or sometimes just the foot) - but they are known without, when they look more like a simple handled cup. I did wonder if these might have been punch cups, but often those had a more barrel shape to the body.
Silber & Fleming show plenty of custard cups, but all have the very short stem leading into the foot, so I'm inclined to think that if these are for custard then they'd certainly be first half C20 examples.
The decoration is cut, but a very meagre sort of cutting, and yes, you're correct, they are glass

- but without any lead content - so very utility orientated, and therefore no ring.
At the sort of height that you describe, I really can't think what other use they might have - perhaps someone else might have other thoughts.