Hey Carl,
Thanks for the response. Mine looks too big to be 5/16" but just a shade under 3/8". Is the size i.d. or o.d. of the line? As I said initially, mine is just a fraction smaller than 3/8" o.d., I'm talking less than 1/64" smaller. But again that's the o.d. The original line is gone, and I don't know what size it had. The vent is definitely 3/8", but with the corrosion it's kind of hard to tell what the original was on the pickup.