@lilygiesen probably a 15mm keychain, however those are a bit more difficult to find, so using a regular round keychain with a triangle start should work, or you could use a larger keychain, however there will be excess metal on the sides if that makes sense
@lilygiesen Hi! I know I'm not the person you asked, however I've gotten my keychains before off of amazon. There are a bunch of different kinds in bulk that aren't too expensive, just make sure you double check the size of the clasp before buying it 🙂 otherwise you can always check your local craft/sewing store or dollar store, they might have as well.