The bcm KeyMod 4 inch Picatinny rail section, nylon - black is a rail section made of lightweight impact resistant polymer, it includes mounting hardware is made of corrosion resistant stainless steel. Made to the mil-standard 1913 Picatinny arsenal specifications and features a snag resistant design, while retaining mil-standards specs. The self-contained assembly, eliminates the possible loss of mounting hardware and rail fits all KeyMod interface mounting surfaces..