The Advanced Technology AR-15 Steel Mil-Spec Castle Nut is a durable and reliable component designed to meet the needs of AR-15 enthusiasts. Constructed from high-quality steel this castle nut is virtually indestructible ensuring long-lasting performance and dependability. Its versatile design is compatible with commercial military and hybrid buffer tubes making it a perfect fit for most AR-15s and AR variants. Featuring a sleek black finish this Mil-Spec castle nut combines strength and style for your firearm. Please note it is not compatible with 308 rifles.