Fits standard 58mm baskets, like VST or IMS. Independent of Portafilter.
Made a new one because i did not have the right magnets for the other models.

Magnets 4mmx4mmx4mm are pressed into the holes. 4 are sufficient in my case. 

Open Source

FreeCAD model included, so you can change the Magnets to whatever you have around. Very simple design and model

Printed with supports. 0.2mm