I have a set of Kimball Midwest carbide hole saws that have proven amazingly useful have proved. Well there were a few sizes I didn't have and getting those sizes from them would have cost me hundreds of dollars. So I realized what the hell is wrong with them. Well they were worse than I expected. I only used a 35mm bit and it's set to a 1/4" corner. The centering nozzle broke immediately. I should have known something was wrong because she rocked a lot more than I was used to. ... So I replaced the racquet with one from a good set I have and carried on. When the carbide tips finally made contact with the metal, everything seemed back to normal. It was similar to our other beats. But then, about 1/8 inch, it started squeaking loudly. I poured some oil on the racquet and held it in place. But it looks like I've already used up whatever sharpness the bit had because the other 1/8 to 1 inch took 4 times as long to get through. I checked and all the tips were still there. I had to drill another hole and wondered if it would be the same pattern. Instead, the first 1/8 inch took even longer. Probably a full minute. I heard a squeaking noise and oiled liberally, but it was like the saw just wouldn't cut anymore. And suddenly there was a click and a few more. Before I knew it, there wasn't a single carbide bit left on the cutter. The bits I got from Kimball Midwest have held me through dozens of holes even in thicker metal. I guess I should have expected a set at 1/8 the price from a big brand to fail so quickly.