lancer420 :
rubix_1011 :
Both tubing and fitting size is defined by ID and OD (inside diameter and outside diameter). You will need 2 fittings for each component (inlet and outlet).
While the sticky is a bit old, the same content still applies. Some of the components used as example are rather outdated, but the concepts remain exactly the same.
So, just make sure the fitting and tubing has the same inner diameter and outer diameter?
Yes, but also be aware that flexible tubing and hardline tubing cannot use the same fittings - they each have specific fittings to be used with the correct tubing. This has everything to do with the type of tubing being used with the fittings, all should be compatible with any watercooling component (G1/4 thread, not to be confused with fitting ID or OD).
And yes, research and learn on your own; see what is out there and make sure it all makes sense before buying. Understand what you need before you buy (or blindly take the advice from someone on a forum)...you may or may not be getting information from a knowledgeable source.