I use vinyl tubing, 1/2" on 1/2" barbs, never had a leak either (sure, doesn't mean it won't happen
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One thing to note: The confusion with barb thread size and barb barb size stems from the fact that the ID is measured on the thread side, whereas the OD is measured on the barb size, because, logically, it corresponds to the ID of the tubing used. 3/8" thread side matches 1/2" hose side, and 1/2" thread side matches 5/8" hose side (actually, not sure about the latter one, could be 3/4", but whatever it is, I use some of it in my loop
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