Sometimes I need to cut a few holes in sheet metal or thin sheet iron. Nothing extravagant: I'm not a machinist. But when you need a hole saw, you don't want to screw it up or spend hours drilling. These hole saws have performed admirably the few times I've used them. Of course I apply lubricant (prerequisite of a mechanic friend). β’ Two additional exercises are good. β’ The spring tension of the drills seems adequate. β’ I would really like to know enough to know what rotation speed to use for which materials. (Hint: a diagram might help.) β’ The case is decent enough to last, but not what I would call "refined". My little quibbles: β’ They are defined and entered in the metric system, not in English. No big deal, the dimensions match the rough work they do. But they are not English. β’ I have added a table on the cover for each item to give its dimensions. Just to make it easier to find the right size. See photo. β’ Your claim that it is a "three-lobed design" can be verified by examining the teeth closely. But the 16mm and 19mm saws have 4 and 5 teeth respectively - not a multiple of 3 like the others - so these two saws are missing some "blades". work), but this is a good set of ten standard size hole saws. If you need it, they will work.