馬格納德

NOTE: This solution is intended to be used with one or more manufactured products.
A Magnerd is a rubber band with a magnet attached. Printing requires flexible filament.
Taking measurements then trying to match the numbe in Customizer will probably yield unexpected results because the values are relative rather than absolute.
Tree-like supports (as provided in Meshmixer, Ultimaker Cura and Flashprint) work with the filaments suggested and can be used for the retainer ring aperture. I wouldn't recommend adding them to the iide of the barrel at any barrel size because they can be quite difficult to remove from inner surfaces. Don't expect supports to work if you try to print using a spongy filament.
My recommendation for a powerful but small magnet to use for Magnerds is Michaels PROmag Neodymium.
There are a couple of presets in the included .JSON file that don't seem to be usable by the Thingivee Customizer. The values of these presets are included below. Belt diameter can be set independently of presets so its value is the same for both. You may want to download both the .SCAD file and the .JSON file so you can access these features in your own itallation of the latest Opecad.
An example .STL file is included that was created in Opecad using the .SCAD file's default settings which are suitable for the PROmag Neodymium magnet.
The fit preset (PROmag Neodymium) is the same as the default setting. That magnet is 6.3mm (.25 inches) X 3.04mm. I also have a some larger neodymium magnets (13mm X 2.5mm) for which the 2nd preset works well. I have no affiliation with any seller or maker of magnets.
Below are the two presets.
ProMAG Neodymium:
"APERTURE": "yes",
"APERTURE_DIAMETER": "0.63",
"BAR": "no",
"BARREL_DEPTH": "4.6",
"BARREL_OUTER_DIAMETER": "3.8",
"BELT_DIAMETER": "4.4"
13mm X 2.5mm:
"APERTURE": "yes",
"APERTURE_DIAMETER": "0.68",
"BAR": "no",
"BARREL_DEPTH": "4.8",
"BARREL_OUTER_DIAMETER": "7.7",
"BELT_DIAMETER": "4.4"