Of course, the Quality of the Manufacturing is Important but besides that the Most Important Distinguishing Features are:
- Geometry of the Receiving Port you are using.
- Threads Call Out on the Fitting and Receiving Port, count per inch and total length of Threads.
- Material the Fitting is made out of for purposes of Chemical Inertness, Temperature the Fitting will be used for.
- Pressure the Fitting will be Required to hold.
- Size of the Tubing the Fitting will be holding.