Fortis Manufacturing, Inc. Lightweight Enhanced AR15 End Plate, K1 System (Tapered) Castle Nut, Gold Finish LE-BLK-K1-GOLD The SI Multi-Function End Plate and Anti-Rotation Castle Nut are designed to update and upgrade the often neglected castle nut and endplate system. 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. With the vast amount of aftermarket...