Compression fittings typically consist of a three-piece set, with each component having a specific function to work together to achieve sealing and fastening:
Fitting Body: The main component, with an internal tapered bore (matching the taper of the ferrule). One end is a threaded interface (e.g., metric or imperial thread) for connecting to equipment, valves, or other pipelines; the other end is for inserting into the metal pipe to be connected (usually copper or stainless steel).
Frrule: The core sealing component, generally made of brass or stainless steel, in an annular tapered shape (taper matching the tapered bore of the fitting body), with sharp cutting edges (1-2) on the inside. During installation, the ferrule is deformed by compression, and the cutting edges embed into the outer wall of the pipe, forming a "mechanical interlocking seal."
Nut: The fastening component, which, through its threaded engagement with the fitting body, pushes the ferrule into the tapered bore of the fitting body when tightened, forcing the ferrule to deform and fit tightly against the pipe and fitting body, ultimately achieving a seal.