Ring Resizer
thingiverse
Update: I am still using this design, reprinting a new one every 6 months when I lose or break it. I have lost weight since posting this design, so I have added Medium and Large sizes. I've also put them at the angle I print them (22.5 degrees from vertical). This is a shim I designed to resize my wedding band. It is sized for my 6.5mm x 21.5mm id wedding band, but you may be able to scale it to fit your ring. At my wife's suggestion, I printed it standing up, like a half moon, with support. This provides strength to the rims so they don't break off.
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