I needed to print this for my outboard engine as the original nut cap got destroyed. It fits very tightly to the bolt as I don't want to lose it. You can control the tightness by printing it a few percent bigger or smaller.
I printed it with 100% infill to make it sturdy and so far it works as planned.
I tried other ready nut caps models from all over the internet, but many were very painful to tighten the bolt. I also needed that the butterfly wings have sort of a neck to avoid hitting the engine construction.
The butterfly wings are intentionally not too wide so the user doesn't have too much leverage or strength to deform the plastic around the bolt or nut.
The author marked this model as their own original creation.