This is a magnetically mounted frag plug rack for marine aquariums. It was printed in PLA, but I suggest ABS or PETG for the longest life.
Uses 32mm x 2mm rare earth magnets, available from numerous online sources. Mine came from Amazon.
The magnets were coated in aquarium silicone, then glued in their holders. After several days to dry they were coated with multiple coats of black spray-on plasti-dip. For my next build, I'll use the solid plasti-dip and simply dip in the magnets.
I'm hoping that will seal them enough to last, but no promises.
Note: Fits most plugs, but not the 1/2" ones. Holes are 10mm, which is a good fit for most of the plugs I have found. I'm using the Oceans Wonders coral frag plugs in the picture: https://www.amazon.com/gp/product/B06Y6DYQXW
See also my other frag rack: https://www.thingiverse.com/thing:2672511
In order to get it to print flat, there are some angles from the magnets to the main frame that can use support to look nicer, and the top of the magnet holders as well, so run support on the main print.
Print two Mag holders, and four caps for each unit.
Be sure to seal the magnets, they WILL rust quickly. I used a layer of silicone sealer, as well as 3-4 coats of spray-on Plasti-dip.