The Faxon Receiver Lock Nut, also known as an AR-15 castle nut, is a precision-machined component that secures the receiver extension to the lower receiver on AR-15 platforms. Built for reliability and consistent fitment, it provides a solid interface for keeping your stock assembly properly aligned.
This is a small part that does a big job on any AR-15 build. Get the castle nut right, and the rest of your stock assembly stays locked up tight.
What the Faxon Receiver Lock Nut Is and Who It Is For
This is a Mil-Spec castle nut from Faxon Firearms, made for builders finishing or repairing an AR-15 lower. It threads onto the receiver extension to hold the buffer tube assembly in place.
It fits new builds, replacement work, and any project where a worn or missing castle nut needs to be addressed. Both factory-style and custom configurations rely on this component.
When properly installed and staked, it delivers dependable retention for the life of the rifle.
Key Features
The castle nut is built for strength and reliable lockup.
- Precision-machined to secure the receiver extension
- Durable steel construction for hard-use conditions
- Mil-Spec compatible with standard AR-15 receiver extensions
- Consistent fitment for factory and custom builds
- Notches designed to accept proper staking
- Dependable retention when correctly installed
Specifications and Build
The Faxon Receiver Lock Nut is manufactured from steel, engineered for long-term durability under repeated installation and hard use. That robust construction ensures the nut holds its lockup when properly torqued and staked.
It is designed to interface with Mil-Spec AR-15 receiver extensions, so it works with standard buffer tube assemblies and lower receivers. This broad compatibility makes it a reliable choice for many builds.
The steel body resists deformation during installation, which helps preserve a clean, secure fit.
Practical Use, Care, and Compatibility
Installation involves threading the castle nut over the end plate, torquing it to spec, and staking it to prevent loosening under recoil. Proper staking is the key to keeping the assembly tight over time.
Care is essentially maintenance-free once installed, though it is worth checking the staking during a detailed cleaning. The steel construction asks for nothing more.
Round out your build with parts from our parts and upgrades collection. The Faxon Receiver Lock Nut pairs directly with a Mil-Spec end plate and receiver extension to complete the rear of your lower.
Small Part, Critical Job
The castle nut is easy to overlook, but it is what keeps your entire stock assembly from working loose under recoil. Cutting corners here invites problems down the road.
A quality steel nut resists the deformation that cheaper parts suffer during installation and staking. That means a tighter, more reliable lockup that stays put over time.
For anyone building or repairing a lower, keeping a correct Mil-Spec castle nut on hand is simply good practice. It integrates cleanly with standard buffer tubes and end plates.
Torque it properly, stake it, and you can forget about it, which is exactly what you want from a foundational component.
Getting the Most From It
Thread the castle nut over the end plate, torque it to spec, and stake it to prevent loosening under recoil. Proper staking is the key to a lasting, tight assembly.
Once installed and staked, it is essentially maintenance-free, though a glance at the staking during a detailed cleaning never hurts. The steel body asks for nothing more.
This castle nut ships direct where state and local law allows, arriving ready for your stock assembly.
It pairs directly with a Mil-Spec end plate and receiver extension to complete the rear of your lower.
For a foundational part, getting it right saves you headaches for the life of the rifle.
For a dependable, correctly fitted stock assembly, the Faxon Receiver Lock Nut is an essential piece. Ships direct to your door, no FFL required.
Reviews
There are no reviews yet.