Eric, remember back to the 1715 fleet spikes, which were square bronze and from before 1715. As were the square sheathing nails. Also the Jupiter wreck, San Francisco y San Antonio 1659, which has square bronze nails. Bronze square nails and spikes date back to Roman times, as do round and iron spikes. Mostly square spikes, and bronze were used. Some are cruder than others, which might help date them. This spike does look very well made, which might make it 1700s to 1800s. The only real way to date a spike, is to date the ship somehow, like with coins, and that still doesnt exactly match, but back then a ship usually didnt last 20 years.