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.
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