Somehow or other, I ended up with a machinist’s background. Given my
druthers, I’d have rings sized to tenths.
Unfortunately, I don’t think there is a canonical list for ring
sizes. I’ve been looking for years, and all the charts I’ve found
either conflict with each other, or have traceable errors to an
earlier list. What’ll really blow your mind is that sometimes the ID
of the sizing ring for a given size can be as much as 25-40 thou
different than the OD of a mandrel for the ‘same’ size. I’ll bet you
even money that if you mike three different mandrels in your shop
for a given size, all three will come back with different OD’s.
Standardization? Ha! measurements by millennia.
On the other hand, it’s important to remember several things:
(A) humans change size. Even if you do mike the finger accurately in
the morning, an hour later, it’ll be a slightly different size. And a
third size by dinnertime. So the best you can hope for is
’comfortable’, which can often be ± as much as 20-30 thou.
(B) Fingers aren’t really round. They’re sort of square-ish. So
getting an ‘accurate’ ID on a round band really won’t do much good
in terms of the levels of accuracy you’d normally run into.
© The width of the band radically effects how its fit is perceived
by the wearer. The wider it is, the tighter it feels, regardless of
the actual ID. Some of the wide (6mm+) rings take about a half-size
jump to get them to feel right. (a “6” turns into a 6.5, for
Yes, in a perfect world, I’d like to be able to say that all “size
7” rings start out at the same ID, to aid in fitting, but you can’t.
Most of us just develop strategies to deal with the flutter in the
Mine is to get a ring that does fit, regardless of the printed size,
and then measure the ID of that ring, and make the next one to match.
Exactly. So if it came out at .788", the real ring will be.788 thru
the bore, with a bit of chamfering around the ends to make it
comfortable. Of course, that only works if you’re doing one-off
customs. For production pieces, find a mandrel that seems to give you
accurate sizes, and run with that one mandrel being "the’ sizer. A
few (tens) of thou of variation in the ID measurement won’t make much