here is a picture of the back in the middle there is a screw type thing, but it looks like the pins were added to make it a hat pin, thinking it might be brass,
It is definitely a 1937-to-1943 type of US Army collar-disc insignia for Infantrymen. The time-dating is from the form used for attaching it to the uniform's cloth. To confirm the info I've given you, go to the following webpage and scroll about halfway down it. Dating Metallic Insignia: Collar Disks