I think I have all the swagelok fittings, tri-clover fittings and solenoid valves to replumb my brewery in stainless for my automation retrofit project. swagelok tube fittings are all 1/2". There is an Ebay Store named Online Metal Supply. They have .049 wall 1/2" OD 304 Stainless Steel tubing for $5.33 a 4' length. It seems like a pretty good price. I also noticed that they have the same tubing in .036 wall for roughly double the price. Is there any reason why I should not use the .049 wall tubing? It would save me roughly $5.00 per 4' length and the ID on the .036 tubing would only be 13 thousanths larger.
ID would be .026" bigger (two walls remember) .402 vs .428. That results in a 13% increase in internal cross section. You'll notice the difference where the ferrules bite into the tube further reducing ID. With the thick wall this will be your area of greatest restriction. With the thin wall that restriction will likely be in the swagelok fittings (1/2" fittings have a .41" ID bore). Of course this means that the benefit of the larger ID tube is not as great as it would at first appear just by comparing tube size. Since your flow rates are not critical I don't think it's worth the extra expense. You're also unlikely to be making too many bends. Not enough tight bends that it would be a pain to use the thicker wall anyway. Save yourself the money and go with the heavy wall.