This is the next evolution of SI’s Ultimate Dust Cover (UDC). The upgraded design, with its double injection mold and overmolded rubberized soft-sealing lip, is designed for improved sealing of your .223/5.56 AR’s ejection port to better protect against dust, debris, and water intrusion when the port is closed. The patent-pending True Seal lip seals the port more tightly compared to traditional cover designs. It comes pre-assembled with all parts needed for quick tool-less installation. An adjustable detent screw is included to compensate for wear to the upper receiver. It’s also designed to be impact-resistant and completely silent during operation.