This is an oil breather vent filler cap for a 1935 to 1947 Ford V8 according to other listings.  I have 3 with a single ring embossed in the top and 6 with two rings in the top.  Please specify when purchasing if this makes a difference. Some of these look like they've never been installed but have some surface rust from traveling around in a box for decades.It needs cleaned. Free shipping, usually same day.