Suppose you had to drive a boatload of sharpened stakes into the ground. Sometimes, the ground is very hard and when you pound for long enough, the stakes split or mushroom.
I've seen metal caps that are placed over the end of the lumber to be pounded upon. The caps take the impact & protect the lumber (usually). They are of course specific to the cross section of the stake being driven.
Does anyone here know what these things are called?