Antque metal social security card

Has an s in each top corner with an eagle in the middle and underneath says "As registered with U.S. Government Social Security No."

Then there is a box witht he ss # and below that is my grandfather's name "Fred Oscar Kullgren" and below in small font is :Buschs Jewelers" 

It appears to be engraved in brass but I'm not sure of the metal

Back is smooth