Designed to fit Quad Rails or larger diameter rails like a Daniel Defense MK18 Omega or similar while leaving the top picatinny rail section exposed. Rail-Rap Heavy Standard Length: 6″ | Diameter: 1.75″ and up. You can also use the Heavy model on your M-Lok / slim rails and it will cover the entire handguard including the top picatinny rail. The Rail-Rap Heavy is made in the USA DuPont Kevlar TEX-80 thread BPG proprietary DuPont Kevlar Bungee cord rated to 800 F