I'm going to be tapping an aquatube to g1/4" threads. I've read in different places that a 11mm or 11.8mm drill bit should be used. For those that have thread tapping experience, which one should I use? Does it really make a difference? Also since I live the US a drill size would be best. I was thinking 7/16" would be good since it's the next major size down from 1/2".