his MDX handguard is the same one featured on our PDX and MDX series firearms. Whether you’re looking to add a different length handguard to your current PDX/MDX, or want to have an enhanced rail system on your HK rail height & style upper receiver, the MDX handguard delivers on function and durability. It features hard coat anodizing for increased wear and corrosion resistance, QD mounting points on each side, and M-Slots on five sides. These hand guards are only compatible with Maxim Defense PDX/MDX receivers and those with HK MR556 mounting styles.