u/Ash_D

I'm building a batch of train whistles as gifts, and I am looking for ideas on how to incorporate a small hidden compartment bored through its center.

My first idea was to slice the end off and embed some magnets into the cap, but I don't think that will be a strong enough closure. I'd like these whistles to be clipped onto a pack/worn around the neck and not worry about it getting bumped and having pieces lost.

Any ideas?