Just getting started: what is it with metric motor shaft diameters vs. english diameter propellers?

Build DIY ROVs
1

I am in the early stages of planning out a simple, 3-motor ROV. I’m am thinking of using some 800kv (-ish) brushless outrunner motors with 50/55mm propellers, like these.

The problem I am running into is that while brushless motors seem to always have metric diameter shafts (3mm, 4mm, 5mm),. most of the boat props seem to have inside diameters measured in fractional inches (like 3/16"). Do I care? I’d be mounting the props with a compression-style prop adapter.

My prior experience is with quadcopters with propellers that bolt directly to the motor casing, so I haven’t had to worry much about this in the past.

2

Kind of a “Lost in Translation” moment I understand. Bushing city or machinists niche area im thinking. Personally id run a drill bit followed by a reamer to a size I could bush the prop to the unmolested motor shaft o.d. A bushing that was readily availible would be ideal of course. Kind of a critical area for prop balance understood.