BCM ORAT52513 A/T Optic Riser 525-13 Black Anodized 13 SlotsA T Optic Riser 525 13 is approximately 5 3 4 long and covers the entire length of an upper receiver and offers one more recoil slot than the upper. This riser has 13 recoil slots (14 lugs). It can be used with any combination of sights, NVG, or thermal which would fit on an upper receiver and the additional slot gives the user some spacing flexibility. Ideal for layering magnifiers and other enhancement systems with red dot optics, BCM A T Risers