This is a customizable step-up ring I made using OpenSCAD, reusing some code from my customizable swirly bokeh filter. You can make any ring from 37mm to 90mm.

Sometimes, the upper thread may be a bit thight. If that's the case for you, I suggest playing around with the end tolarance setting under the advanced tab.

Also, if you want to use this ring for heavy filters, like I do, you should tweak the settings in the advanced tab to make the part stronger. I recommend using PETG to make the it more durable.

Note: This script cannot make step-down rings.