Vortex Precision Matched Rings start with certified USA 7075-T6 billet aluminum and are held to an extremely tight tolerance of .0005 using a precision Computer Numeric Controlled (CNC) mill. Precision Matched Rings are kept in pairs throughout the manufacturing process ensuring perfection from one set to another. These Vortex rings are then serialized, vibratory tumbled, hand-bead blasted and finished off with a military standard Type III hard coat anodize. * Height measurements in drop down selector refer to the height of the center of the rifle scope tube from the top of the mounting rail. NotesThese Vortex Precision Matched Rings position the center of the riflescope tube at the height provided above. It is measured from the base of the mount to the center of the riflescope.Will only work with Picatinny spec mounts-will not work with Weaver mounts. Sold two rings per package. Hex wrench included.Limited Lifetime Warranty