This Gen3 stripped upper receiver features a precision machined billet aluminum construction, a black hard coat type III anodized finish, and its compatible with all Mil-Spec AR-15 parts and accessories. NOTE: This model is not compatible with Geissele Modular rails. Requires dust cover, forward assist, charging handle, gas block, barrel, handguard, gas tube, muzzle device and BCG (Bolt Carrier Group) to complete.