I have a Rex Griggs inline CO2 reactor with 5/8" barbs up for cost of shipping. However you could always switch out the barbs for any other size as they are just threaded in with teflon wrapped fittings. Also went ahead and switched out the method he used to insert the co2 tubing with my own which is simply drill a larger hole and insert a small plastic fitting. That you can just slip the co2 tubing over. The entire setup cost me around $30 to build. However I am no longer running CO2 so figured someone else might get some use out of it. I ran it for about 6 months and never had a single drip of water leak out. I am thinking $12 should cover shipping. If it is less I will refund if it is more that is my fault and I will cover it.