This is a TROY Sling Mount, model SMOU-M4S-00BT-00.
The Troy OEM M4 Sling Mount replaces the factory M4 carbine receiver end plate" incorporating ambidextrous quick detach swivel mounts. Includes heavy-duty quick detach push button swivel. Made from hardened aircraft aluminum with stainless steel push button.
Features:
Hardened aircraft aluminum
Ambidextrous quick detach swivel mounts
Heavy-duty quick detach push button swivel