Product DescriptionThe Ergo 4971B castle nut is a durable steel, black-finished castle nut designed for AR-platform builds. Built to help secure the receiver extension (buffer tube) in place, it is compatible with commercial, military, and hybrid buffer tubes and fits AR-15 rifles and other AR variants.Product Highlights Steel AR-15 castle nut for securing the receiver extension/buffer tube on AR-platform rifles Black-coated finish for corrosion resistance and a clean, low-glare look Compatible with commercial, military, and hybrid buffer tubes Standard Mil-Spec CAR-style castle nut design Fits AR-15 and all AR variants (per manufacturer listing)Specs Brand: Ergo Manufacturer Part Number: 4971B UPC: 810049123000 Product Type: Castle nut Platform Compatibility: AR-15 / AR-platform variants Buffer Tube Compatibility: Commercial, Military, Hybrid Material: Steel Finish/Color: BlackDisclaimer: 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.