Advanced Technology A5101020 AR-15 Castle Nut - Mil-Spec Steel, Black Finish

The Advanced Technology A5101020 AR-15 castle nut is a mil-spec steel component engineered to secure your buffer tube and receiver extension with the reliability that modern AR builders and maintainers expect. If you're assembling an AR from the ground up, performing a stock swap, or refreshing your lower receiver, a quality castle nut is non-negotiable—it locks everything in place so your action cycles smoothly and safely. This one meets mil-spec standards and arrives in a durable black finish that resists corrosion.

Castle nuts are easy to overlook until you need one. They're the unsung anchor between your tube and receiver, and mil-spec steel construction means you're getting a part built to the same durability standard that has proven itself in thousands of rifles across decades. Paired with a proper wrench and a staking tool (or a gunsmith), it takes minutes to install and will hold solid through thousands of rounds.

Whether you're a first-time builder or a seasoned tinkerer, having the right hardware on hand keeps your AR running like it should. Advanced Technology's focus on precision manufacturing translates to tight tolerances and consistent performance—exactly what you want in a component that bears real duty.

Key Features

• Mil-spec steel construction for proven durability and reliability
• Black finish for corrosion resistance
• Precisely manufactured to tight tolerances
• Essential for AR-15 buffer tube and receiver extension assembly

Specifications

Frequently Asked Questions

What is an AR-15 castle nut used for?

A castle nut secures the buffer tube (or receiver extension) to the rear of your AR-15 lower receiver. It threads onto the tube and is then staked to the receiver, creating a permanent, reliable connection that keeps your stock or brace assembly in place during firing.

Is this castle nut mil-spec?

Yes. This Advanced Technology A5101020 is manufactured to mil-spec steel standards, ensuring it meets the durability and dimensional specs used across military and civilian AR platforms.

Will this work with any AR-15 lower receiver?

Castle nuts are a standard AR-15 component. Compatibility depends on your receiver's threading and your buffer tube spec, which are typically standardized across mil-spec AR builds. If you're unsure about your setup, consult your receiver or kit documentation.

What finish is this castle nut?

It comes in a black finish that resists corrosion and matches standard AR furniture.