This is a ProMag known as the Recoil Pad, model PM088.
This AR-15 6 position carbine stock 'U.S.' marked recoil pad adds 1/2" length of pull to AR-15 / M16 carbines equipped with six 6 position collapsible stocks as fitted to the M4 Carbine.
Features:
The pad features U.S. and ordnance flaming bomb markings
The pad is manufactured from injection molded chemical resistant black rubber
