GBRS Group Lerna Mount Kit Fits. 91" Optic Centerline for faster target ID" regardless of gear/ equipment obstructions" i.e.. EarPro/Comms headsets" Gas masks/ CBRN" and Night vision use. A higher Optic allows for a more athletic posture and "Heads up" attitude that enables the end-users to maintain a vertical spine which translates to body armor or "presenting plates" to the threat. This "Heads up" style allows for faster processing speed and increased situational awareness. Features of GBRS Group Lerna Mount Kit Fits: 2.91 Optic center line" Package Contents: GBRS Group Lerna Mount Kit Fits