This is a dimple die made to form sheet metal.  The largest part of the dimple is ¾" and the flat at the bottom is ½".  I tested it on .062" thick aluminum sheet and it worked great.  I did make several versions of the die before settling on the one posted with no guide for alignment.  What I found was the hole has to be drilled smaller than the desired finished hole due to the amount of stretch it goes through while being formed.  I was looking for a hole of about .230" and I wound up using a 5/32" pilot hole to achieve a finished product with a useable hole.  

You can see in the pictures, I used a shortened finish nail as an alignment guide.  The hole in the die is just the correct size to catch the head of the nail and secure it.  I used a 6" vise to squeeze the dies together and form the dimple.  The dies are made of PLA-Tough and they are printed with 100% fill.  I have not tested this on sheet metal yet, but I believe it will work on 20 gauge or thinner without issue.

UPDATE-2/13/26 I have tested this die with 16 gauge sheet metal and it worked great.  But I had to use a cheater pipe on the vise handle!