Zero gap rings are typically used in the second scraper grove and are two overlapping rings, thus the name zero gap. I would highly advise coating the skirts, along with the top to nearly eliminate scoring. If half of the top is ceramic coated and you put a torch in the center you will see a hole blown in the uncoated half several seconds before it gets through the coated half. Coatings will not cure a bad injector not matter what some of the companies tell you. If you have any fly cutting or any other machine work done be sure to break the sharp edges as they WILL cause hot spots.