LBE Unlimited ARCNUT Castle Nut 4140 Steel Black Phosphate AR-15
https://www.tandktactical.com/shop/765857617329-lbe-unlimited-arcnut-castle-nut-4140-steel-black-phosphate-ar-15-24513
https://www.tandktactical.com/web/image/product.template/24513/image_1920?unique=a84e0f7
The Castle Nut is constructed of 4140 steel with a phosphate coating. It is compatible with your AR-15.
