TROY Industries PG Sling Mount, Quick Detach, Flat Dark Earth SMOU-PGR-00FT-00 The Pro Grade Rifle Sling Adapter enhances M4 stock reliability by sliding over the existing receiver extension" eliminating the chance of castle nut rotation. The Troy PGRSA allows the addition of an ambidextrous Q.D. swivel attachments without modifying the rifle. Constructed of hardened aircraft aluminum with a stainless push down button Q.D. swivel" this sling mount installs in less than two minutes with no gunsmithing required.