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