re: What to use to make a rattle rattle?

10-24 nuts were about the right size for the dumbbell-shaped rattle. Black peppercorns will go in the larger ring, or maybe small pieces of 10-24 bolts (I have a nice bolt-cutter from a previous project). The small octagonal ring was too small for me to (successfully) turn a cavity in it, so I’ll try again using solid wood rather than a segmented design for that next time, and start a bit bigger.

Stainless is an interesting idea, but much harder to work, and my local hardware store didn’t have any small bearings, regardless of the material, so I’m improvising.