The Ergo Grips AR-15/M16 M4 Receiver Castle Nut is a precision-machined steel component designed to securely lock the receiver extension or buffer tube to your lower receiver. Built to mil-spec dimensions with stakeable pockets and slotted wrench flats, it delivers a consistent, repeatable fit on AR-15, M16, and M4 platforms while working with commercial, military, and hybrid buffer tubes.

This castle nut is ideal for new builds, upgrades, or replacing worn hardware on AR-pattern rifles. Its durable black steel construction supports long-term reliability for range use, training, and general shooting, helping maintain proper tension and alignment in the buffer system. Shooters who value correct dimensions and dependable hardware will appreciate Ergo Grips’ attention to detail and proven manufacturing quality.

Key Features:

• Manufacturer: Ergo Grips
• Model: AR-15/M16 M4 Receiver Castle Nut
• Material: Steel
• Color: Black
• Compatibility: AR-15/M16/M4 receiver extension tubes; works with commercial, military, and hybrid buffer tubes
• Design: Stakeable pockets with slotted flats for use with a standard armorer’s wrench
• Use: Secures receiver extension/buffer tube to the lower receiver for stable operation