There are some old black bolts from this old hardware store, that has been a hardware store since 1885. This is one of them. These were discovered stored away upstairs. We have brought them downstairs to make them available for restoration projects, etc.
The head on this 5-inch bolt measures 1/2 inch. The 5/16-inch threads cover only 1 1/4 inch of the shank of the bolt.
Let us know if you need a square nut. (Those are still here also.)