Protect your hands and rails from your muzzle with this Aero Precision M4E1 Threaded 5.56 Mid Pencil Barrel w/ ATLAS S-ONE Handguard Complete Upper Receiver. These AR15 Upper Receivers built by Aero Precision feature an advanced handguard attachment system that is incredibly secure, yet easy to remove. Then, this Aero Precision M4E1 Threaded 5.56 Mid Length Barrel Complete Upper Receiver provides a front and rear Picatinny rail for weapon accessories like laser sights, lights and other attachments.