Yes, for sure, protecting the material should be taken into consideration, but it depends highly on the kind of material that the washers are made out of, so I provided no information so far about that. I am under the assumption that mine are stainless steel, however after reading your suggestion, I tried to see if they're magnetic and they are, just a bit.


I can just imagine myself getting my angle grinder to buy something

Have you considered a magnet? They're available in many sizes and shapes on AliExpress and can probably fit somewhere inside the 3D design. Unless you're going for stainless steel washers, but I assume those are too hard to stamp.
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I am pretty sure mine are stainless steel, similarly to many commercial 'steel backups', which is quite good for rust and general robustness compared to plain steel. However, stainless steel can still be magnetic and it's a pretty cool idea to use magnets that I had not thought about so far.
However, the washer has to be held either from the top or the bottom (side is too shallow I think). From the bottom is tricky because then you'd be hammering onto the magnet, not sure if they're made to withstand that. From the top won't work, because the top is not covered by the 'outside' part of the jig, instead by the (removable) inside. We need a way to stick the washer to the outside part instead.

I have one idea which would require re-seating the washer for applying the numbers though, since I'd put a magnet in that location roughly. So you would need to do the number first, rotate the washer by 180 degrees and then do the words.



Thanks for the feedback! Yes, I mentioned where I found the idea in the starter post, at least I think that the BlockMit guys are the ones who came up with it I just recreated a new jig in Fusion with parametric values for everything, compared to their Tinkercad model that was hard to modify.