Of course, the quality of the manufacturing is important but besides that the most important features of all fittings are:
- Geometry of the receiving port you are putting the fitting into.
- Threads 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.