Seals
Sorry, not the animal... or or the singer...
the mechanical kind:
Conflat seal: article
KF seal
Wire Seals
differentially pumped seals
Threaded Seals
Gaskets, O-rings
Metal
copper
silver
Viton, also known as FKM (a type of rubber)
Viton o-rings have gas-permeability that acts as a leak under UHV conditions. Thus this type of seal is forbidden in level 1 and level 2 vacuum systems and requires a variance to be used in level 3 systems.
Flanges