This thing I made here is called a nail header. It's use is for finishing the making of a nail.

When you're about done with making the nail, it goes in to that square hole and the left over mass of the rod you half way cut it from( and then broke it from the rod into the header) becomes the head of the nail.

https://www.furaffinity.net/view/34805847/ Here is a diagram I've drawn for that in the past.

I've been meaning to make my own header for a while now, but I always put it on the back burner.

This tool is made from a bit of rail road scrap. The piece in mind is called a "Rail Anchor. Very good high carbon steel, significantly higher carbon content than a rail spike.

Just don't go prying them from under track to get them. They need to stay there.