Instrumentation fittings are widely used in fluid or gas transfer applications such as refineries, chemical plants and food processing plants.
The male end of a double-ferrule instrumentation fitting has a recessed counter-bore which matches the tube OD being used, plus an inner cone.
The seal is made between the front ferrule and the cone. The tubing is held in place by the swaging action caused by the tightening of the nut, which forces the front and back ferrules to bite into the tubing, firmly holding it in place. This allows for the use of un-flared tubing with these connectors.
Instrumentation Fittings
The single-ferrule instrumentation fitting is similar, but has a larger front ferrule and no back ferrule. The sealing method is also similar. Both types of instrumentation fittings are commonly available in stainless steel and brass.
Instrumentation fittings have UNEF (extra fine) threads and sizing is determined by the outside diameter of the tubing being used.