I saw fidget toys and spinners so I tried to make one of my own.
The bigger one is 25mm, the smaller one is 20mm. I'm only 5ft0in so I thought that would be small enough for someone my size. Other people have made caps for the bearings so I made some of those too. They might need to be sanded smooth.
Amazon has loads of different sized bearings, I designed these around "694Z Metal Shields Sealed Deep Groove Ball Bearings 4 x 11 x 4mm 10Pcs" so the dips on the sides are 11mm wide and 4mm deep.
I don't have a 3D printer so I can't test it. Sorry about the bad pictures.