This is a quick ring i designed, i couldn't find a ring that i like so i made my own! ;)

Feel free to scale to size, i recommend printing the first 10 or so layers just to see if it fits and you can scale freely without wasting filament until you are happy with the fit (original is DIA 20.5mm ID)

It does require a bit of sanding to get a nice smooth texture, i used 320 grit till the layer lines disappeared and then move to 1200 till smooth to the touch (To get that last bit polished up from the 1200 grit, rub the ring on a piece of fabric i found that anything polyester will work, it wont damage the material and this way you don't need any polishing compound, just use a bit of elbow grease)