Reproduction WW 2 German u-boat cap badge.
Not sure which u-boat used this device.
Stamped brass with 2 prongs on back for fastening. 
Size is 2 3/8 x 1 11/16 inches.

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

Repro WW2 German U-boat cap badge u-? Kriegsmarine Sub Submarine