Sightron SIII10 50x60mm Tactical Elevation Knob 19 MOA Black MOA. The full knob rotates with the knob depressed to fully re-adjust travel. Once set depress to rotate to your "lock-in" position to re-set to zero each time. Return to zero after re-adjustment is easily accomplished by turret indexing. The engraved mark shows that the knob has been re-indexed to zero and that the knob has a pre-drilled cross-hatch to aid in recognition of zero. The etched mark also allows you to easily calculate and transfer range. Specifications for Sightron SIII10 50x60mm Tactical Elevation Knob 19 MOA: Manufacturer: Sightron Color: Black Features of Sightron SIII10 50x60mm Tactical Elevation Knob 19 MOA Tactical Elevation Turret 74001 1/4 MOA Click Value 19 MOA Engraved Compatible with: SIIISS1050X60LRMOA SIIISS1050X60LRIRMOA SIIISS1050X60LRMOA-H SIIISS1050X60LRIRMOA-H For A Compatible Tactical Windage Turret See 75001 Package Contents: Sightron SIII10 50x60mm Tactical Elevation Knob 19 MOA Sightron 74001: SIII10 50x60mm Tactical Elevation Knob 19 MOA Black MOA