I designed this Chaotic Pendulum a few years ago but just realized did not publish. Most Chaotic Pendula are made of metal to give it a lot of inertia. Plastic has a low density, so this was designed to use 3/8 hardware to give it mass. Bearings are just standard roller blade/ fidget spinner bearings, though the ones pictured have built in spacers. The mounting rod is just a 3/8 lag bolt with head cut off. Use washers or other spacers needed.

Video: https://www.youtube.com/watch?v=puKKnkeJTXw