A buddy of mine asked for a small keychain that has a socket wrench head on it so he can tighten and unscrew different joints on his camera tripod. I went and mocked up a quick tool for it (about 5/16 wrench size). Fits snug but not too tight when around head since I wanted the walls to be as thick as possible (it's plastic, not metal).
Be sure your layers are solid around the hex part. If there are spaces and gaps, the plastic will compress and the tool will just spin around the nut.
I might suggest inlaying fiberglass or carbon fiber in the thumb grip if you have access to a markforged (which I printed on).
I've printed in both nylon and onyx (markforged material), and they work fine.