Cantilever spacer that increases the height of the #22M68 mount by 1/2" and moves the optic 1 3/4" forward. Pairing the #22M68 mount with this extension spacer provides a perfect co-witness with the standard front sight on the AR15/M16/M4 platform when mounting directly to the flattop rail. The forward extsion of this spacer provides extra room for use with rear BUIS or magnifiers.