The back is marked with a letter 'P" inside a circle. Researching online, I found info stating that hallmark to belong to Carl Poellath of Germany. The history on the Carl Poellath company states they began venturing into military badges during the 1st World War, and ended badge production during WWII. Going by that, this insignia pin would be from the WWI to WWII time frame.
The previous owner wrote "21st Infantry WWII" on the cardboard holder. The pin does have an older look to it so I believe that time frame to be correct. The pin has double clutch holders on the back. All enamel and metal pieces are present with no chips or cracks.
The pin is part of a large collection of insignia pins that I purchased at an estate sale. It is attached to a small thin cardboard square. Any writing on the cardboard was put there by the previous owner and that's great because I can't imagine how long it would take me to look up and obtain information on over 700 pins. I'm using his information. He was the expert, so hopefully the information is correct.
The pin is in great vintage condition but there are a few faint scratches, too small to give you a measurement on.
Buyer to pay USPS First Class Mail parcel delivery charges of $4.15. Shipping is from Nevada.
I do combine shipping on multiple items purchased. However, my web host is not set up to calculate multiple item shipping costs. At checkout, you will be charged full shipping price on each item purchased and I will refund the appropriate amount of over payment.