Fidget spinner using US pennies as weights, in several different sizes. There are very small ridges that hold the bearings and pennies in place, designed to fit the chamfer on Bones Reds bearings* (they have a smaller chamfer than the VXB bearings* I also have). The pennies and bearing should stay in place without glue and can be removed.
Older pennies (made before 1982) are made with copper and should be almost 25% heavier. If you want to modify the tolerances, you can do so in Onshape.
Filaments: Protopasta Stainless Steel*, Protopasta Magnetic Iron*, Intservo Glow in the Dark* (the protopasta metal filaments are about twice the density of regular PLA)