The Armaspec ARM6521-BLK Self-Retention Castle Nut/Al brings a smart upgrade to AR-15 and M4 buffer tube assemblies. Built from lightweight aluminum with a hardcoat anodized black finish, this “no stake” castle nut uses a patented self-retention thread design that locks firmly in place without the need for staking or messy thread locker. The result is a clean, repeatable installation that helps keep your receiver extension secure through extended use.

This model is ideal for builders and enthusiasts who frequently change stocks or buffer tubes and want tool-free removal and reinstallation. Its mil-spec compatibility ensures a proper fit on standard AR-15/M4 buffer tubes, while the low-profile, grooved exterior offers positive purchase during installation. Whether you are assembling a new rifle or refreshing an existing build, this castle nut reflects Armaspec’s focus on practical innovation and dependable performance.

Key Features:

• Manufacturer: Armaspec
• Model: ARM6521-BLK Self-Retention Castle Nut
• Material: 7075-T6 Aluminum
• Finish Color: Black Hardcoat Anodized
• Compatibility: AR-15/M4 Buffer Tubes
• Unique Features: Patented Self-Retention “No Stake” Design, Tool-Free Installation
• Weight: 0.015 lb (approx.)