I found this forum trying to find what kind of error coins I have, but I did have fun reading some threads, especially 'How far back can we go". Before I noticed 26 pages, I thought I could help with a 1906 indian cent... haha! Anyway, pictured on the left is the dime (excuse my point-and-shoot camera) with a regular on the right. I can barely tell the year by eye, but I'd say it's 2004 or 6.

I have a quarter that's about the same, but it's not as striking, since it's about the same diameter as a regular, but it's still flat-edged and thicker than normal. They seem related to brockage or a die-cap error, but I don't know how it could be the same on both sides.

Welcome to the forums!

I think your dime is some type of planchet error, but it might be damage after minting.

Looks like an attempt to make a ring. You put the coin on its edge and start tapping with a spoon or small hammer. Then drill out the center. They probably stopped when they saw it would be too small.