Since these backup sights were never meant to be the primary aiming system, we did away with the dual apertures and went with a single .160 aperture which is small enough for accurate shooting yet large enough to still be of use in low-light. Accepts all aftermarket front sight post replacements with MIL-SPEC dimensions. Both front and rear backup sights lock in the folded and deployed position. The durable construction and solid mounting system guarantees you’ll stay on-zero.