6mm ID 9mm OD... for the 6mm comp fittings
10mm ID 14mm OD... for the 10mm comp fittings
(Refer to Koolance's tubing page - their fittings are designed for their tubing.

I see your point, yes they accept 1/2" ID tubing, but only if you're prepared to use 1.25mm wall'd 1/2" tubing. Relatively useless to the majority.

Marci,
That's not correct. Legris has them in native G3/8. Just visit their website and look for compression fittings.
Cool - will add them to my list of suppliers for fittings then...