The Armaspec Self-Retention Castle Nut in Black (brand part no. ARM6521-BLK) is a billet aluminum castle nut built to lock securely onto an AR-15 buffer tube without the staking most standard castle nuts require. Armaspec designed the self-retention feature specifically to solve the common problem of a castle nut backing off under recoil, which can loosen the whole stock assembly over time. Machined from aluminum instead of stamped steel, it also holds a cleaner finish that matches the rest of a billet-parts build. Because it self-retains, installation is simpler than a traditional castle nut, since it doesn’t require punching or staking the receiver extension threads to keep it in place.

Key Specifications

• Machined from billet aluminum instead of stamped steel for a stronger, cleaner-finished part.
• Uses a self-retention design that locks onto the buffer tube without staking.
• Reduces the risk of the castle nut backing off under recoil, a common issue with unstaked standard castle nuts.
• Finished in black to match most factory and Cerakoted AR-15 lowers.
• Simplifies installation since it doesn’t require punching or staking the receiver extension threads.

Frequently Asked Questions

Do I still need to stake this castle nut? No, the self-retention design locks onto the buffer tube without staking.

What problem does a self-retaining castle nut solve? It reduces the risk of a standard castle nut backing off under recoil, which can loosen the entire stock assembly.

What is this castle nut made from? Billet aluminum, rather than the stamped steel used on most factory castle nuts.

Buy the Armaspec Self-Retention Castle Nut

Order the Armaspec Self-Retention Castle Nut from our Lubbock, Texas gun shop for fast, direct shipping. It’s a simple upgrade that keeps a stock assembly locked down without the hassle of staking. Browse more AR upper parts from Armaspec.