Each Classi jar has a vacuum pump built into the lid, to pump out the air and keep your food fresh longer. There is no separate gadget to loose or use. Just press the button. The smaller button next to it releases the pressure. It's not a twist top. The lid is a silica gel sealing ring, which is air tight.
Don't hide this luxurous glassware in a closet. Made from high borosilicate glass, they are beautiful! Show them off on your counter top for everyone to admire.
You get four sizes, for each of your needs.