Vortex Cantilever 30mm Riflescope Ring with 1-inch Offset & Lower 1/3 Co-WitnessIdeal for use alongside your Vortex red dot sight, the Vortex Cantilever 30mm Riflescope Ring with 1 inch Offset and Lower 1 3 Co Witness was engineered to allow you to co witness your front sight using the attached optic. It has a 1 inch offset that positions the scope in a forward position, allowing for correct eye relief and head placement. The cantilever ring positions the center of the riflescope tube positions the center of the scope 1. 57 inch