TacFire MAR039 Castle Nut Black Steel AR-15 Buffer Tube Threading

The TacFire MAR039 Castle Nut provides secure buffer tube retention for AR-15 platforms with precision-machined steel construction. This essential lower receiver component ensures proper buffer tube alignment and prevents loosening under recoil stress. Built to mil-spec dimensions, it delivers reliable performance across all AR-15 variants.

What Makes This Different

Unlike aluminum alternatives that can strip or deform, this castle nut features hardened black steel construction rated for thousands of cycling operations. The precision threading matches standard buffer tube specifications with zero tolerance variance. Six castellated slots accommodate standard staking tools for permanent installation, while the corrosion-resistant finish maintains functionality in harsh environments.

Key Features

• Hardened black steel construction resists thread stripping and deformation
• Mil-spec threading (1.148"-16 TPI) fits all standard AR-15 buffer tubes
• Six castellated slots enable proper staking for permanent retention
• Corrosion-resistant black finish prevents rust and oxidation
• Compatible with carbine, rifle, and pistol length buffer systems
• Precision machined to SAAMI specifications for consistent fit
• Standard wrench flats accommodate armorer's tools

Field testing demonstrates consistent torque retention under rapid-fire conditions and temperature extremes from -20°F to 140°F. The steel construction maintains thread integrity through repeated disassembly cycles, making it suitable for competition rifles requiring frequent maintenance. Law enforcement agencies specify similar components for duty weapons due to their reliability under stress.

Technical Specs

• Material: Heat-treated carbon steel
• Finish: Matte black oxide coating
• Thread pitch: 1.148"-16 TPI (mil-spec)
• Overall diameter: 1.25 inches
• Height: 0.375 inches
• Weight: 0.8 ounces
• Compatibility: All mil-spec AR-15 lower receivers
• Installation: Requires castle nut wrench and staking tool

This castle nut represents essential insurance for any serious AR-15 build or maintenance project. Professional armorers stock multiple units for inventory management, while the affordable price point makes it practical for backup applications. Quality steel construction eliminates the guesswork common with inferior alternatives.