Downloadable template for 8 different models of three-prong earring nuts.
Print them out on paper or sticker paper. The printout should work both for US Letter and A4 paper, but make sure to select a real size option so there’s no scaling going on.

Cut out the nut model you want to use, apply to your silver or gold sheet, 0.4 mm or 26 gauge recommended, better if you just rolled it down to size once or twice, so it has some work hardening spring to it.

Saw around, file, drill a hole for the post and you’re ready for finishing in your preferred way. Use the tips of round nosed pliers to curl the prongs in. Adjust so that the volutes apply some pressure on the post.

Enjoy the most secure nuts you’ll ever meet!