Fortis Manufacturing, Inc. Lightweight Enhanced AR15 End Plate, K1 System (Tapered) Castle Nut, Gold Finish LE-BLK-K1-GOLD The K1 system features a tapered castle nut that seals itself onto the end plate. This ultra precision snug fit allows the castle nut to seat and seal itself into place without the need of staking the end plate. No ratcheting" no set screws" no backing out and no failures.