I've seen some discussion about edge distance marking tools (including in Kitplanes
magazine), and I figured I'd throw in my idea. I was looking for an easy way to do this about a year ago, and had the idea of 3D printing a tool with holes in it for various diameter marking pens.
Here's some pictures. It has holes for four different set distances-- 1/4", 5/16", 3/8", and 7/16".
Here's a link to the .stl file for printing.
This link will only be good for 7 days per my sharing policies, but if you find this post later and want a copy, just send me a PM.
If you want to print one, I suggest slicing it at 0.2mm slices. I've printed it on my Prusa i3Mk3S with PETG with the platen at 85C and the extruder at 250C.