Sea level pressure is 29.92 and a vacuum is, as Peter said,
…well - nothing, as the pressure is “vacuumed” out.
As to quality, I don’t like the mass produced metal findings
that don’t hold up. Usually they’re not substantial enough to
hold up under day to day wear. Give me a good quality piece,
particularly a good quality setting. Mass produced is fine if the
durability is there, but I’ll take quality metalsmith work over
any of that any day of the week!