13/16'ths and judicious use of the venerable file will yeild the best possible fit. You want it as snug as posssible (no slop) but not too tight, that would interfere with getting a good seal and even tigntening. I also dimple my stainless washers to follow the inner contour of the vessel. This creates even presure on the o-ring for a leakproof connection. Just sayin, Wayne and his boyz rock too.
What do you mean "no Kidneys"???, WTF now I gotta drink less beer...
Join the Automation sub forum in Electric brewing for a discussion of components and control systems. I did!!!!