Found this square nail on the beach near where a civil war ship sank off the coast. It's about six inches long and about 1/2 inch wide at the top. On the other side it's about 1/8 inch wide all the way down.
I do know from here that in earlier times they used brass nails in shipping. I have also learned that a nail was a very valuable thing. People out west during the migration would burn down a house just to take their nails when they moved to re-build again. Welcome to t-net David and Happy Holidays. You may wish to try the Forum on here called "What is it" or try the search feature as a research tool.
Happy Hunting
TnMtns