hyd-air olive type compression fittings consist of a nut, and olive and a body. They are extensively used along with brass, copper, aluminum, nylon and bundy tubing.
when assembled, the olive pinches onto the tube at both ends and forms a leak proof joint. The fittings can be dismantled and re-assembled as frequently as

the o-ring face seal fitting (or orfs fitting) consists of a nut, a fitting body, an o-ring and a sleeve. The flat faced sleeve is brazed onto the tube (or the tube may be flanged to 90°). The o-ring is held captive in a precision machined groove in the fitting body. When the nut is tightened onto the fitting body, the o-ring

Cutting ring fittings, also known as flareless bite type fittings or compression fittings, are the most widely used bite type fittings in the world.
the fitting consists of a body, hardened cutting ring (ferrule) and nut. On assembly, the ferrule grips the tube in position and the cutting edges of the ferrule "bite" into