Thread Size For C02 Reg Output

Hello all, I'm in process if setting up a 75g planted tank and need a bit of help. Plan on doing a build thread when I get it up and going. Tank is cycled, semi planted (more to come when I get them out of QT) and stocked with 1 BNP, 2 Giant Danios and 3 Platys to keep the cycle going.

Recently acquired a used UP-Aqua C02 regulator that has a flex line between the regulator output and the bubble counter. This arrangement is not what you would call convenient and I want to plumb the bubble counter directly to the output port.

I sorted through a variety of brass fitting I have on hand only to find none are the right size, apparently SAE vs what I presume are metric fittings on the reg.

Anyone know the correct size I would need to make the conversion?

 

So a trip to the hardware store reveals the correct size was 3/8 MIP. Got parts and reassembled to my liking using a bit of thread sealant on all junctions. Now need to calibrate the pH controller and get the system installed.