Another 5M top shelf revision.
The author remixed this model.
Revised the top shelf designed by JakeP3d to hold two or three 2.75X30 mm magnets. You can print them with or without nubs on the left side. You will need to loosen or take off the upper B guard plate. The one using 3 magnets definitely has a strong enough hold. I put roughly 2 pounds on it and it has held while printing.