Type A corny keg PRV valve thread size?

[aangel]

Hi! I'm curious about repurposing the PRV valve threading in my ball lock kegs. Well what I really want to do is attach a variable pressure relief valve directly to them, kind of like the picobrew fast ferment adapter...but I'd like it to be variable and not just fixed 7psi.

I've seen a bunch of $5-$12 variable pressure 1/4 and 3/8" NPT pressure relief valves on amazon...but I'm fairly certain that the keg PRV isn't an MPT threading. Does anyone know what type of thread it uses? Google isn't answering me.

 

[DarkNoonBrewer]

I believe its 9/16-12. Its a very strange thread size, but Im sure they chose that for safety reasons. For what you want to do, you may have to find a metal PRV and weld a fitting to it. Otherwise, you'll be on a lathe to make a custom threaded fitting.