Nogent Expert Series knives. These knives have 4 serrations per mm on the cutting edge. The cutting edge is extremely sharp, but the mini serrations cause the edge to get traction on the smooth skin of plum tomatoes giving thin slices without damaging the fruit. I first saw this knife on offer from Lee Valley Tools, but these knives are available from many sources if Googled. I have tried many different knives over the years, but this 4 inch blade is the best I have found for tomatoes so far.