Product Description The TacFire MAR039 castle nut is a steel, black-finished locking nut designed for AR-15 carbine buffer tube assemblies. It is used to secure and tighten the receiver extension (buffer tube) to the lower receiver, helping maintain a stable and reliable stock/buffer tube setup. Built for straightforward installation, it&';s a practical replacement or build component for .223/5.56 AR-15 platforms. Product Highlights Steel construction with a black finish for durable AR-15 buffer tube assembly use Castle locking nut design helps securely retain the receiver extension (buffer tube) to the receiver Compatible with .223/5.56 AR-15 carbine stock/buffer tube setups Designed to meet Mil-Spec fit standards for dependable integration Compact, lightweight component ideal for new builds or replacement parts Specs Brand: TacFire Manufacturer Part Number: MAR039 UPC: 811261021914 Product Type: AR-15 castle nut / buffer tube locking nut Material: Steel Color: Black Overall Length: 1.375 in Net Weight: 0.5 oz Compatibility (as listed): AR-15 .223/5.56 carbine buffer tubes; fits commercial and Mil-Spec buffer tubes Disclaimer: We strive to provide accurate and up-to-date product descriptions, specifications, and images; however, errors or omissions may occasionally occur. We are not responsible for any inaccuracies or discrepancies in the content provided. If you notice anything incorrect or unclear, please contact us so we can correct it. When in doubt, we recommend verifying details directly with the product&';s manufacturer.