Remington 870 Supercell Recoil Pad. Photos and info from TexasArmor84 from Remington 870 Forum:

Remington Supercell Recoil Pad Remington 870

Remington Supercell Recoil Pad Remington 870

Remington Supercell Recoil Pad Remington 870

Remington Supercell Recoil Pad Remington 870