Sat outside for a while. I’d weld them to each side of a 12 foot 4x4 3/8” thick square steel and bolt it to the floor of my garage to hold up the roof.
they look like the parts that bolt to a table jig to keep a part from moving while it is being welded or machined or whatever.
Those brackets are to nice to throw away. Could actually be vase holders for a fancy Cadillac. Heres my 1920 Cadillac cup holders. The long ones are for the rear seat passengers due to the 36 inch legroom.
Oxygenated stopping blocks. Retention brackets for establishing the angle of a dangle. Under the shoulder boulder holders. They could actually be rumbleseat lid stops from an older big car. Any backstory like where,when, what car?