It fits 20x6x2mm magnet in the bottom so you can put it on some metal surface.

I incuded STEP file that you can change it as you can.

If you decide that you want to use the STL file make it a bit bigger. Instead of 19mm make it 22mm, or make it easier print the PLA or PETG g.code file.

I suggest print with supports on the bed.

(You will probably have to modify it a bit, but it was easy)

Happy printing!