A #12 drill is 0.01890" diameter. A 3/16 drill is 0.1875" diameter.
Search the web for "drill chart".......they can be downloaded for free. It should have hole sizes for numbered drills (1-60), fractional drills, and lettered drills. (Who knew there were so many drill sizes?
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) The chart will definitely come in handy.
Also, if you are going to ream to final size, you will have to drill an undersized hole.....typically 1 drill size smaller for the hole sizes we're dealing with, and then ream the hole to final size.
Building an RV....at least the 3/4/6 where ALL the holes had to be drilled....kind of like getting a PhD in hole drilling/reaming, while picking up a Masters Degree in de-burring.