Also depends on the type of thread and barb style used on the radiator. Radiators sold for the European market generally use G1/4 fitting which normally require a "O" ring under the fitting to make a proper seal.
Radiators for the US market on the other hand can, and do several different type of thread specs, anywhere from G1/4 inch to 3/8 FPT (Swiftech). Some radiators such as the BI series can be fitting with several different types of fittings, so it's always best to check with the maker of your radiator to double check just which type of fitting can be used with your radiator and what is their recomemded method of sealing the barbs.
