These offset inserts work only in Burris Signature Rings. They are offered as a matched pair in three different offsets, a set of all three and a box of ten each (Product number 712472). One insert half is slightly thicker and the other slightly thinner than standard. Swapping the standard inserts with a pair of offset inserts will move the point of impact approximately 5" at 100 yards for the .005 inserts, 10" for the .010 and 20" for the .020. This will allow a gun to be sighted in that cannot be zeroed with the available windage and elevation adjustments in the scope. For serious shooters, the optional offset inserts allow a scope to be brought almost to complete zero, then using the windage and elevation adjustments only for the final, fine adjustment. This keeps the erector tube centered in the scope for improved scope clarity and performance.