Other people on the thread suggested that security might have thought it would be some kind of club-like tool.

I just had a butter knife confiscated at an airport security. Butter knife, no edge, no point, a regular butter knife. And it was right as I was rushing to get to a next flight, I didn't try to protest. It really pissed me off.

I've had small size swiss army knives get through lots of times, and also get confiscated a couple times.

If something is iffy, I find it's best for it to have a confusing, non-knife like shape. Like for instance - folding scissors. I've always had these go through, even though it's just as dangerous (if you wanted it to be) as any knife with a 2 inch blade, but the knife will definitely be confiscated, and so far the scissors have been okay.

You can bring "sharp edges" in. I have a credit-card-sized toolkit that includes a knife that is maybe an inch long and I got it in hand luggage multiple times. The regulations specify a minimum blade length.

And he mentioned washers for stamping words on them, not a big metal plate.