Fun little Simon's cat fridge magnets.
Default size vary from 80 to 100mm in heigh and 5mm in thickness.
Glue a magnet on the back (CA or neoprene glue). I used a single 10x2mm per item, I don't recommend smaller magnets as they may be to weak (or use multiple of them). Also pay attention to the center of gravity of each models.
STLs don't come with a magnet insert, that way you can use a different size than me.