I know it is a US Military Button, just not sure which war?

[teak]

Found in my Neighbor's yard, it has the screw backs, I am thinking WWII?

 

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[willie d]

Definitely post WWII. The WWII collar devices had screw on backs. I'm not absolutely positive but I think it is possibly Vietnam era at the latest. http://wardogmilitaria.com/index.php?main_page=product_info&cPath=55&products_id=1731

 

[teak]

Post WWII. The WWII collar devices had screw on backs

Actually these are screw backs, should have shown a better picture. Thanks for the info.

 

[MilitariaCollector]

Most early WWII collar discs were screwback. The screwbacks were used from WWI up to WWII. Clutchback collar discs were used in WWII, and were the most common type found. Your insignia has 2 clutchback pin posts and appears to be 1 stamped piece. This style dates from WWII, and surplus ones were used up into the Korean War. The post Korean War - present day clutchback collar discs are a three piece construction with 2 clutchback pin posts.