Reproduction WW 2 German U-boat cap badge.
U-71 used this device. 
Made of brass with 2 prongs on back for fastening. 
Size is 1 7/8 x 1 3/8 inches. 

Listing is for one pin, photo shows front and back.

Repro WW 2 German U-boat Cap Badge U-71 Kriegsmarine Sub Submarine