Re: 7/16" coupler for water?
I've never heard of 7/16" pipe. If that's the actual outside diameter of the pipe, then it probably has a different name.
For "iron pipe size" (IPS -- galvanized steel, black iron, brass, ABS, PVC), what's known as "half-inch" pipe actually has an outside diameter of about 7/8". 3/8" nominal has an outside diameter of about 5/8". 1/4" nominal has an outside diameter of about 1/2". 1/8" has an outside diameter of about 3/8". The threads on steel pipe are tapered; the very end of the pipe is slightly narrower than the portion where the threads meet the unthreaded portion.
For "copper tube size" (CTS -- copper, most plastics except ABS and PVC), 3/4 is 7/8", 1/2 is 5/8", 3/8 is 1/2", and 1/4 is 3/8". CTS pipes are typically not threaded, but rather use "slip" fittings that are either welded (via solvent or solder) or compression fittings.
Are you sure it's not really a standard size? You can't go by the actual measurement; you have to take the measurement and convert it to a nominal size.
The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.