This is a single WW2 Navy Officer Overseas Cap Device - Sterling.
It is marked STERLING and Vanguard maker marked on the eagle and the anchors as well as 1/20 10k GF on the anchor.
It is a pinback.  The eagle wiggles a bit but it is securely fastend to the anchors.
This device measures approx. 1 1/4" x 1 1/4"
 
Domestic shipping is via USPS Ground Advantage with tracking.