The Ergo castle nut (brand part number 4971B) is a steel replacement part finished in black, built to work across commercial, military, and hybrid buffer tubes. It fits the AR-15 and all AR variants, making it a safe, universal choice whether you’re building a new lower or replacing a worn or damaged factory castle nut. Getting the castle nut torqued down correctly is essential to a solid, rattle-free stock or brace installation, and this steel replacement gives you a durable factory-fit option to do that job right.

Key Specifications

• Fits the AR-15 and all AR variants.
• Compatible with commercial, military, and hybrid buffer tubes.
• Machined from steel.
• Finished in black.
• Torques down for a secure, rattle-free stock or brace installation.

Frequently Asked Questions

Will this castle nut fit a commercial buffer tube? Yes, it’s compatible with commercial, military, and hybrid buffer tubes.

What is this castle nut made from? Steel, finished in black.

Buy the Ergo Steel Castle Nut for AR-Platform, Black

Get a secure, factory-fit castle nut for your build. Order from our Ergo lineup of gun accessories and parts and our Lubbock, TX team will get it ready as soon as it’s available to ship.