This is a Bravo Company Sling Mount known as the KeyMod, model BCM-KMSM.
The BCM Gunfighter KeyMod QD sling mount is the perfect mounting solution for attaching slings to rifles with KeyMod rails.
Features:
Low-Profile
Fits standardized KeyModâ„¢ interface mounting holes
Requires three KeyModâ„¢ attachment hole mounting points
All steel construction