This site has dimensions of 'Tiffany-inspired' keyrings, which shows the circle as being about 1 and 1/16th" in diameter. I'm assuming the long measurement is from the top of the ring to the tip of the charm.

This large one measure 4cm in diameter.

This one is 'about 1 in' across.

Here's a bigger one, 1.75" diameter.

Googlefu. I haz it.

That's great, Jan, thanks!

Hmm. Okay, so 1" diameter, probably (1 1/16" is likely only available on a custom basis). I'm trying to just eyeball and guess dimensions--I wonder what the gauge is, and how big the balls on the end are. 8g for the ring part, maybe? That's about 3mm. Then the balls are, oh, maybe 3/8", 10mm, something like that?

(I have no idea what to buy for a friend for her birthday, so I'm thinking maybe this.)

If you go hit some jewelry stores or even the jewelry departments of larger dept. stores, you may well find a knockoff that you can eyeball. Everybody makes imitations of those.

I've seen and sold bunch of these (and even owned a steel knockoff of one) and would say you're probably right on 3mm for the ring and maybe a touch large on the balls (heh heh), perhaps closer to 8?

Ok, going by this top-down picture and counting pixels, the diameter of the ball is about 4/13 the outside width of the ring, so if the ring is 1", then the balls are probably 1/4". The wire is 3/35 the width of the ring, so probably actually 1/12", 11 or 12 AWG.

Please tell me you're going to put the silver tag on it and use it in a piercing.

er, 4/12 is not 1/4. The balls are probably 1/3".