EPC (Ejection Port Cover) is based on TDP dimensions, with thoughtful Forward Control touches. Billet machined from 7075 aluminum, and hard coat Type III anodized, it incorporates features we think many will find useful. EPC has two "tabs" flanking the cutout for the port cover spring. These tabs allow the EPC to rest on the upper at a greater angle when it's in the down/open position, which provides more space between the port cover and lower receiver. Their job is to better allow the user's finger to get underneath the port cover when he wishes to swing it up/close. Another feature is a shallow circular depression on the side of the EPC to provide texture tactile feedback to the user's finger when he's closing the EPC. A flat surface provides nothing to the user to differentiate one surface from another, it also provides no traction. A shallow circular depression on the left side of the EPC does both. We incorporate flat surfaces with care as they have their uses . In this case, EPC's exterior surface is treated as a control surface, where a flat surface rarely makes sense. EPC is compatible with TDP spec upper receivers.