You, my friend have a lot to learn.
The 1/4" part refers to the thread size used in the blocks, pumps and resovoirs-G 1/4"-which is pretty universal although a few parts like the pump in your first post use unthreaded barbs where the soft hose is pushed on and retained by a sprung steel or plastic clip. Barbs like that won't accept hardline pipe work, even if it's the correct size-at least not without some modifications.
Fittings will have two dimensions, one for the internal diameter of the hose, the other for their thread size so a 1/2" G1/4" fitting will ONLY accept hose of 1/2" ( 12.7 or 13mm depending on how exact they are) internal diameter ( ID ) but will screw into any pump/block/res that has standard G 1/4" threads.
Some fittings will only accept a certain hose size ( internal and external diameters ) so it's ESSENTIAL to ensure hose and fittings are matched for size and, making matters more complicated still some give the sizes in inches, others in millimetres.
Depending on exactly how the system is designed you may need more than straight fittings, using 90 degree ' elbow ' fittings can greatly reduce the length of hose needed to connect parts, making for a neater system. The downside is that these 90 degree fittings introduce some flow restriction and should be used sparingly.
And then we have to consider the pump.
And the radiator/s.
And the hose size.
And the exact positioning of each part.
My point here is that we'll offer what help we can here, but you really need to do more research yourself before spending a single cent on parts.
It's easy to make expensive mistakes with watercooling, even kits aren't suitable for every purpose and purchasing individual parts is a minefield of potential mistakes waiting to happen.
Do yourself a favour and take a closer look into the subject, YouTube has plenty of ' how to ' videos, while the Newegg and EKWB websites also have a mass of valuable info on the subject.
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