Then a couple years ago, I made a few rings as part of a workshop at Hadar's.
So here's what I've discovered so far...
I took two rings that should be about as perfect in specific sizes as can be. Both are ring blanks from Rio. A size nine and a size seven.
The size nine happened to fit my thumb perfectly.
So I took my ring sizer...
... and found that the size nine on there also fit my thumb perfectly.
Off to a good start.
But things went south quickly. I took my ring sizer and put size nine on my steel ring mandrel and it showed up as a smidge over 8½.
Then I put my ring sizer and put size nine on my plastic ring mandrel and it showed up as a wee bit past size 9.
And then I did something magical. Ha ha ha! I took my digital calipers and measured the inside diameter of the rings.
BTW, if you get digital calipers, look for ones that have this thing on top (that's for measuring interior diameter). I got these at Harbor Freight for less than $20 (use their coupons!).
When I googled "ring band measurement chart", I found that you can tell a ring's size by the interior diameter (d'oh!). This looks like a good chart. Here's another chart by Art Jewelry Magazine. According to this (and similar charts), you can tell a ring's size by the interior diameter.
Low and behold, the size 9 came to 18.8mm and the size 7 came to 17mm (is supposed to be 17.2mm, but this is good enough for me considering the alternatives).
So for now, out go the measuring methods of ring mandrels and I shall begin to make use of my digital calipers.
Tomorrow I get to measure/size the 100 rings I just made for the show I'm doing next week. At least I feel better about the results now. Only half the rings in this shot (47 actually).
So that solves one half of the equation, but what about the other half... fingers. What are people using to measure their fingers? We'll look at that another day. Sigh...
Okay, that's it for today. Back to work (so much to do to prepare for this show!).