(since I believe the sight glass requires a smaller hole)
From bargain fittings, the sight glass and ball valve require identical holes. 13/16 is idea, then use a deburring tool or similar to clean the opening. It is a tight fit for the nipple, but far, far better than drilling a hole too large.
I just used a hole saw (3/4") for mine....it worked super. Of course, the hole was too small, but I opened it up a bit with a dremel, and got a nice tight fit.
Linear Mode
