Ultimate Arms Gear Sling Swivel Stud Adapter To Weaver Picatinny & Stud Rail Mount QS Quick Shoe System for Heckler & Koch HK G3 MP5 USC MR556 MR762 Mounts to Existing Swivel Stud. Provides a 3 Slot Picatinny Rail Section for Rail-Mounted Accessories such as Bipods, Lasers, Lights etc. Features A Side Swivel Stud To Maintain Continued Use of Shoulder Strap. Easy to Install. Weight - 3oz.