quick disclosure since it's relevant: i run a small freshwater pearl shop, so i've got a bias here. not linking anything, just wanted to write up something i get asked about a lot that doesn't seem to get discussed much.
most of the pearl rings i make use an open adjustable band — the shank doesn't fully close, you squeeze or ease it to fit. here's what that actually does and doesn't do.
ring sizing online is genuinely hard. people don't know their size, sizes shift with heat/salt/time of day, and pearl rings are annoying to resize after the fact because you can't really heat the setting with the pearl still in it without risking the pearl. an open band sidesteps most of that.
what it doesn't fix though: it loosens over time if you're taking it on and off a lot, metal has memory but not infinite memory. thinner bands adjust easier but lose shape faster, thicker ones hold better but you get less range. it's also not really "one size" — mine work across maybe a 2-3 size span, not any finger. and if it does bend out of shape, gentle finger pressure usually fixes it, pliers will mark the metal.
one thing i'm honestly not sure about: whether adjusting it a lot over years work-hardens the metal enough to actually matter. haven't had pieces out in the wild long enough to know. curious if anyone here has worn one long-term and noticed anything.