I made a keychain with a hidden loop.
With a layer height of 0.2mm you should set up a pause at layer 38 and put the ring in.
I used this Keychain: https://www.aliexpress.com/item/1005003803735916.html
If you don't have a 3D printer, I sell it on Etsy: https://www.mikebayer3d.etsy.com
The original design is from DrLex
https://www.thingiverse.com/thing:2738211
https://github.com/DrLex0/print3D-FlexiRex
flexi_rex_keychain.stl | 353.5KB |