I have the close quarters dimple dies from Cleaveland. They came with a few copper mandrels, but I’ve found that on anything other than super thin sheet, those just aren’t up to the task (they stretch and break). I’ve always heard that you can just use a finish nail as a mandrel instead, but I can’t find a nail with a head size that works. For the right nail diameter that fits through the die hole, the head is just barely larger and pulls through the die when squeezed. What’s the trick?