I tend to make a lot of things involving embedded magnets so keeping track of polarities is pretty important. I made this polarity bar to help me out. Embedded in the bar are 3mm cube magnets. Print this at .2 layer height and at layer 4.6 you need to add in a pause or filament swap so you can drop in the magnets. There are 12 magnets to install so it'll take a bit of time. Also, you need to add a tiny drop of super glue to each magnet because if you don't the magnets will jump out and attach to the extruder. if you plan on doing it with two different colors like I did then you'll need to do the first filament change at layer 2.2. Super helpful tool if you use a bunch of magnets.