Dremel with sanding and cutting bits (or hacksaw blade and sandpaper)
Heat gun (boiling water might work as well)
2x2 plate legos (2)
hard/14 gauge (-ish) wire
1x8 plate lego (This size is barely big enough for my pinky. If you want it to fit a larger finger, scale this lego up accordingly) Steps:
* Use a dremel or hacksaw to cut notches into the sides of the 1x8 plate
* Heat up the 1x8 with the heat gun until you can bend it into a "U" shape. Wear gloves to protect your hands from burning. If you don't have a heat gun, placing it in boiling water for a few seconds might work.)
* Cut a piece of wire that fits snuggly into the first set of "bumps" at the top of the "U"
* Place one of the 2x2 plates into a vice and cut a "ditch" into the back that is big enough to fit the wire.
* Because the longest plate I had was 1x8, I had to shave down the second 2x2 to allow my finger to fit. If you have a longer plate, you can skip this step.
* Sandwich the wire between the two 2x2 plates
* Fit the 2x2s with the wire into the 1x8
See the inspiration for this ring here