1, pipe thread seal (self-tightening seal), gasket seal.
2. Octagonal ring and elliptic ring seal (applicable to petrochemical industry).
3. Packing seal (O-ring, oil seal).
4. Mechanical seal. Sealants and adhesives.
5. There are more gap seals, floating ring seals, dynamic seals, labyrinth seals and magnetic fluid seals that you don't need. To sum up: use self-tightening, gasket, oil seal and so on.