MPN: APRH100082C


  • Compatible with both Mil-Spec & Commercial carbine buffer tubes
  • Made in the U.S.A.


  • Material: Steel
  • Weight: 0.5 oz.


  • AR-15


The AR castle nut (a.k.a receiver extension lock nut) by Aero Precision is made the highest industry standards in the firearms market. This Mil-Spec castle nut is designed to be a replacement for worn parts or for a new custom AR15 build.

Did you know that "staking" your castle nut is better than simply using blue thread lock? Many people who are building their own ARs are unaware of the significant benefits of staking your castle nut. This AR15 part is actually designed to be staked. The castle nut design features a notched and circular configuration that screws on to the lower receiver extension (also called the buffer tube) and retains the lower receiver extension and the lower receiver end plate in position. The standard mil-spec AR castle nut will have notches cut out of it that resemble the top of a medieval castle tower (hence the name). On the other side of the nut are smaller indentations that face the receiver and the end plate when the AR castle nut is installed according to the manufacturer's directions. These smaller notches are designed for the staking process.

Failure to stake your buffer tube castle nut can have a negative impact on the reliability and accuracy of your firearm. If you own an AR for self-defense purposes, it is doubly important that you are able to rely on the weapon to perform at its peak at all times. In worst case scenarios, failure to stake your castle nut can result in irreparable damage to your AR and possibly to yourself as well.

Staking an AR castle nut is easy and takes all of 60 seconds to complete. Once you've installed the nut at 40 foot-pounds of torque, use a spring-loaded center punch or a standard center punch to force material form the end plate into one or two of the small notches on the nut. This small step will ensure a semi-permanent bond between the receiver end plate and the buffer tube castle nut. This simple step takes only a minute to accomplish, but it can have far-reaching safety benefits for you and your AR15.

Have a question?

Ask an Expert

Reviews (7)

  • Outside Diameter Out of Spec

    Posted by RGCGFMT on 2nd Oct 2022

    This is the only Aero Precision part I've ever had a problem with, and I've used lots of them. The caveat being that it's a relatively small problem. The OD of this castle nut appears to be slightly out of concentricity with the ID. This made use of a standard 3-point wrench difficult. Not impossible, but more difficult than torquing the nut to spec needed to be. Otherwise, the threading, internal fit, and finish are all good. This part is inexpensive and it is not in my opinion imperfect enough to rip back off of the rifle and return. But should I decide to sell this rifle build in the future, I will likely replace this castle nut first. YMMV.

  • Perfect Fit!

    Posted by Unknown on 11th May 2020

    After searching numerous known distributors (all of which were out of stock), Wing Tactical offered this Castle Nut at an affordable price and shipped without delay. the part fit perfectly, completely my stock/brace adapter assembly. Well-packaged, good price!

  • Great Value

    Posted by Cal Perlas on 22nd Apr 2020

    Great quality material at a low price. I am pleased and impressed with this Castle Nut. I will purchase again for sure.

Customers Also Viewed