The person I love has a crafty hobby: crocheting! So she told me about those crochet rings that help maintain the right amount of tension while preventing the yarn from causing to much friction on your finger. She found this ring by karosass1 but I thought something with a hook would be easier to use.

Features:
The ring features a hook with a small gap to facilitate threading the yarn and a small guiding rail so the thread doesn't slip.

Size: 
I provided models with inner circumferences from 40mm to 65mm so you can choose depending on your index fingers circumference (thank you z123carleigh and Amanda for giving me feedback). Just use a tape measure to determine the right size.

Print:
No support needed. The base of the print has quite a small contact area so using some glue stick is recommended in case of first layer adhesion problems. 

Material:
PLA, PETG, ASA, TPU (not too soft), ABS. They all should work fine.

I used polypropylene (Fiberlogy PP Nature) because I like the toughness, the slight flex and the smooth texture. 

Happy printing!

Over two thousand downloads and many makes later I am blown away by all the positive Feedback that reached me. Thanks a lot! One thing I am repeatedly surprised by is the amount of different ways people use their ring. Some to tension their yarn, some as a stress relief, some on there index finger others on there ring finger, some mirrored, some turned by 180 degrees. Also people are wearing them on different phalanges of their fingers.

For my partner and me, there seemed just one obvious way to use such a simple device but in reality there seem to be so many individual ways to use the same simple tool for basically the same simple task. It's a wonderfully humbling experience to see that your thoughts going into a design are not nearly as universal as you think.

edit - 2022-10-16: added sizes 56mm to 65mm and added a .step-file for easier remixing.

edit - 2022-11-13: added sizes 40mm to 44mm for smaller hands.