Smallest ID of tubing

[enaberif]

I know most tubing comes in 3/8s but could you go smaller?

Or would flow be really impeded badly?

[MpG]

There's definitely a little more flow restriction - since your ratio of tubing wall/cross-sectional area goes through the roof, compared to larger tubing. Another issue that is that if the ID of the tubing is small enough, it can actually affect how well components operate (beyond just the issue of flowrate). DDC pumps, for example, needs a certain inlet flow aiming into the impeller to work right (which is why right-angles directly into them can significantly weaken their performance). Impingement-type waterblocks often rely on a certain cross-sectional area of incoming water to operate best, and an incoming stream of water that's only 1/4" wide might not be optimal. I can't find it anymore, but I seem to recall Swiftech used to have graphs for their MCW-60 GPU block, where using 1/4" fittings weakened it's performance, even at the same flowrate as larger sized fitting. Some of Koolance's blocks have separate graphs for 1/4" tubing and larger tubing as well.

That said, I doubt even a worst case scenario would cost you more than a few degrees. If you really need to go 1/4" for clearance reasons, go for it.

[Babrbarossa]

1/4" ID tubing and fitting available at sidewinder
Metal Standard and Compression Fittings

Last time I bought something from there it never came.....

[Sushi Warrior]

You could get much much lower by using other types of tubing not meant for computers, but yeah 1/4 is the smallest size that is still common.

[CanadaRox]

I wouldn't go any smaller than 1/4 in for a cooling system. It should be fine with most pumps designed for 3/8 with the correct barbs (or the wrong barbs and some elbow grease). Beyond that I think you would starting seeing a significant drop in performance.

[Dazmode]

Yes, I have some 8 and 6 mm compression ittings that I got by mistake (good price). I have one guy who take them and got tubing from canadian tire. Everything cost him third of normal size.