Compression Fittings size

[clone38]

3\8" ID - 5\8" OD (10-16mm) or 3\8" ID - 1\2" OD (10-13mm) Compression Fittings

 

[Remmy]

For the flow it makes no difference as they're the same inner diameter. You should choose which you prefer the look of, and also bear in mind that thicker walled tubing (higher outer diameter) can bend tighter loops without kinking so if this is something you need then go for the 3/8"-5/8". I personally use 3/8"-1/2" because I don't need tight bends, I use angled fittings instead, and also I think there is more availability of fittings and things for 3/8"-1/2"

 

[clone38]

Ill be fitting some 90s and 45s in the build just trying to save a wee bit of cash as the fittings are going to cost me .

 

[S_I_N]

dont skimp if ya have to wait a little longer to get it all right its better in the long run.