Back when I worked in a vacuum lab we used copper O-rings between tubes, and the edges of the tubes had a knife edge to cut into the copper. It was pretty expe

Back when I worked in a vacuum lab we used copper O-rings between tubes, and the edges of the tubes had a knife edge to cut into the copper. It was pretty expensive - you’re only supposed to use each O-ring once. We had a big box of them that we’d occasionally send off to recycle.