I like old CPUs and I always need magnets on the fridge. As the old CPUs have a lot of pins at the back, I built myself a housing to click the CPU in.
The CPUs sit tightly in the holder.
There is a 2mm deep cut-out on the back, where a magnet can be glued in. e.g. one from an old hard disk ;)

here are the dimensions of the CPUs
- Intel Core i5-12500 - 45x37.6mm
- Intel i486DX2 - 44,5x44,5mm
- AMD AM486DX2-80 - 44,5x44,5mm
- Cyrix MII-300GP - 49,5x49,5mm

I have printed everything without support. It doesn't look nice on the back, but it works.

I will add more sizes as soon as I find new old CPUs.