TOPIC: 1972 Windsheild Question

Hi,
I had to replace 2 panes (pains) of glass in the windshield of a 1972 Cruisers Inc. Bonanza 21.
In order to do this I needed to completely remove the windshield to disassemble frame.
I would like to replace old hardware with new and that is where my problem is.
It was attached to boat with what appears to be 1/4" threaded bolt with nuts but with a thin square flat plate as bolt head.
Does anyone know what these are called or where I could source them?

I did a search on Thin square head fasteners and found this place.
It's a start ? the screws are metric, but M6 is pretty much a 1/4 inch screw.
us.misumi-ec.com/vona2/detail/221005000987/?HissuCode=SPNSQHSLT-SUS-M6-10

Thank You, that's a great help.
I feel a little silly now that I just didn't use right search words.