Any Davis swirls are hard to find given their short run and often difficult to discern features. Trusting a random seller on ebay to know what they are would be a mistake. Only one of two I have off this type that came right from a Davis source. Some literature can be found on them and there are some examples in the new West Virgina swirl book as well. Under loupe a pin and 2 micro pin touch spots.. 01" oor