This is a ProMag Sling Attachment, model PM254.
The adaptor plate installs between the stock and receiver on Remington(R) Model 870(TM) shotguns to allow the use of a single point sling. Ambidextrous mount allows sling to be mounted to either side of the stock. Constructed of aluminum alloy with a black" hard-anodized finish.
Features:
Installs between the stock and receiver
Allows sling to be mounted to either side of the stock
Aluminum alloy construction