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1 an is 1/16
3 an is 3/16
5 an is 5/16
10 an is 10/16 or 5/8
16 an is 1 inch. or 16/16
this is the pipe size. the inside diameter depends on your wall thickness.
3/16 is 1.875 inch so take your wall thickness, double it, and subtract it from 1.875.