The TacFire MAR039 Castle Nut Black Steel For AR-15 Buffer Tube is a compact, steel locking nut engineered to keep your carbine receiver extension firmly secured to the lower receiver. Built to Mil-Spec dimensions and finished in black, it integrates cleanly with most AR-15 and AR-10 buffer tube assemblies while providing dependable thread engagement and long-term durability.

This castle nut is ideal for new AR builds, routine maintenance, or replacing worn hardware on .223/5.56 carbine stock setups. Its straightforward design supports easy installation with standard armorer tools, helping maintain a stable stock and consistent cycling at the range or during training. TacFire’s focus on practical, reliable components makes the MAR039 a solid choice for shooters who value simple, well-executed parts in their rifle platforms.

Key Features:

• Manufacturer: TacFire
• Model: MAR039 Castle Nut
• Product Type: AR-15 castle nut / buffer tube locking nut
• Material: Steel
• Color: Black
• Length: 1.375 in
• Weight: 0.5 oz
• Compatibility: .223/5.56 AR-15 carbine buffer tubes; fits commercial and Mil-Spec buffer tubes