Out of stock
SKU: EG4971-B
UPC: 810049123000
The Ergo Castle Nut For AR15 Blk is a mil-spec receiver extension castle nut designed for M4-style carbine builds and direct impingement systems. This component serves as the critical retention mechanism that locks the buffer tube assembly to the lower receiver, making it essential for anyone assembling or servicing an AR-15 platform rifle. Whether you're a law enforcement armorer, military technician, or serious civilian shooter building a complete rifle, this castle nut is a non-negotiable foundational piece that ensures your stock remains secure under recoil and operational stress.
Manufactured from hardened steel and finished with a durable black oxide coating, the Ergo Castle Nut For AR15 Blk meets standard mil-spec CAR (Carbine) specifications for dimensional accuracy and material integrity. The castle nut's fluted design allows for quick tightening and removal using a standard armorer's wrench, while the indexed geometry ensures repeatable alignment with receiver extension slots every time. Black oxide coating resists corrosion and abrasion during installation and extended field use, providing reliable performance in diverse environmental conditions without additional maintenance or re-coating.
This castle nut is compatible with all mil-spec AR-15 receiver extensions, including M4 and M16-profile carbine tubes commonly found on patrol rifles, tactical builds, and competition platforms. Installation requires only a castle nut wrench and proper torque technique—typically 39 foot-pounds for standard buffer tube assemblies. Armurers and gunsmiths benefit from the precision machining and consistent fit that minimizes wobble or rotation during assembly, while shooters appreciate the security and repeatability this component provides for long-term reliability and zero consistency. Stock replacement, buffer tube upgrades, or complete lower receiver builds all require a dependable castle nut; Ergo's mil-spec construction delivers that assurance with proven performance across law enforcement and military platforms.
WARNING ⚠️ You must be 18 or older to purchase shotgun or rifle ammunition and 21 or older to purchase handgun ammunition and firearms. Please reference our requirements for ammunition orders to "restricted" states HERE. Always make sure you use the correct ammunition for your firearms. Ammo cannot be shipped to a PO Box. Please reference state & local laws before making a firearm or ammunition purchase.
