Inches are bits of 25,4mm lengths divided into fractions, instead of decimals, which is exceedingly dumb, but with practice, you learn that what you need is 3/8ths (timestamp @14:24) Here is an unsolicited lecture.
The standard runs as
1/8th
1/4th (or 2/8ths)
3/8ths
1/2 (or 4/8th)
5/8th
3/4th (6/8ths)
7/8th
1"
THEN some lunatic decided to divide it up into 16ths, and slid in such gems as 11/16th (which is 1/16ths less than 3/4) because they just can't get away from it, and so many industry standards for piping, hydraulics, machines etc are already in inches. And it simply is easier to divide 25,4mm into fractions of 16, and never think about the actual distance again.
edit: sorry again. You persevered, and what I wrote here is of little relevance!