Premium quality PVC Tubing from Masterkleer.... as used in the top quality kits on the scene.
ID - 7/16"
OD - 5/8"
Bend radius approx 1.5"
This tubing has several benefits to your watercooling enthusiast kit's performance.
It's low cost!
It's ID matches the ID of most 1/2" hose barbs giving a smoother flow path
As it's slightly smaller than 1/2", simply heat up the tubing in warm water before pushing over barbs. Once it's shrunk down, it provides a snug tight seal generally abolishing the need for hoseclamps
It has a very nice bend radius for tight bends without kinking
Altho it's OD difference to 1/2" Tygon etc is minimal, it is sufficient to make for a cleaner looking, less cluttered system