The Strike Industries Ultralight Multi-Function End Plate and Anti-Rotation Castle Nut are designed to update and upgrade the often neglected castle nut and endplate system. Now available in an ultralight 7075-T6 aluminum version that is anodized in color options to customize the look of your AR. While the traditional endplate and castle nut works extremely well in retaining your receiver extension, the peening of the castle nut is not conducive to rebuilding or upgrading. With the vast amount of aftermarket support for the AR system today, SI feels that there's a need for a secure system as adaptive as you are. Enter the MFEP and ACN. The SI MFEP and ACN offers a built-in anti-rota Mfg: Strike Industries