The Advanced Technology Mil-Spec Castle Nut (ATI Outdoors part no. A.5.10.1020) is a black steel castle nut built for AR-15 platform buffer tubes. Advanced Technology builds it virtually indestructible and compatible across commercial, military, and hybrid buffer tube specs, so you’re not stuck matching a nut to one narrow tube standard. It locks the receiver extension securely against the lower receiver, which is what keeps a collapsible or fixed stock from working loose over time. It fits most AR-15s and AR-pattern variants, though it’s not compatible with .308-chambered AR rifles running a different buffer tube standard.

Key Specifications

• Built from virtually indestructible steel.
• Works with commercial, military, and hybrid buffer tubes.
• Fits most AR-15s and AR-platform variants.
• Not compatible with .308-chambered AR rifles.
• Finished in black.
• Finished with e-coated steel for long-lasting wear resistance.
• Made in the USA.

Frequently Asked Questions

Will this work with a commercial or Mil-Spec buffer tube? Yes, it works with commercial, military, and hybrid buffer tube specs.

Will this fit my .308 AR-10? No, it’s not compatible with .308-chambered AR rifles.

How durable is this nut? ATI rates it as virtually indestructible steel construction.

Buy the Advanced Technology Mil-Spec Castle Nut

A loose stock assembly is often just a worn or damaged castle nut, and this ATI nut is a durable, direct-fit way to tighten everything back down across most buffer tube standards. Order from our Lubbock, Texas gun shop and it ships fast to your door, along with more AR-15 parts.