8.5 inch quad rails are hard to find on the market because there are many variations of the different shapes of circular/triangular cap. This quad rail is designed to fits all caps out there but MAY REQUIRE modifications. * The tabs at the end of quad rail are designed to fit different caps, Use DREMEL to cut off the extra caps to make it custom fits your CIRCULAR/TRIANGULAR cap. * 18 slots on each rail. 2 piece drop in style only takes 3 minutes to install. * Made from durable aircraft grade T6 aluminum with anodized finish. * Please note that installing a free float handguard is an involved process that involves additional tools to install; we recommend first watching an instructional video on youtube before installing, or better yet employing an experienced gunsmith