The Trinity Force UL – B.U.S. (Back-Up Sight) can be used as both a backup sighting system for rifle optics or as a primary sighting system. These polymer sights are equipped with an internal quick-deploy mechanism that can be activated by pressing the body of the sight forward along the axis of the firearm.The Trinity Force UL – B.U.S. is designed to attach to any standard MIL-STD 1913 rail system and fits securely using the locking cross bolt and clamp system. To mount the sight, loosen the cross bolt nut and remove it completely from the sight base. Slide the sight onto the MIL-STD 1913 rail, then insert and re-tighten the cross bolt nut, securing the sight to the rail.