These screws are super hard! I did the same thing last year. I was able to drew through/out, very carefully and slowly, with diamond drill bits from HF. It helps to use liberal amount of cutting oil to extend the life of the bits. They have the oil at HF too. After that, for a couple of them I had to use a tap to clean out what was remaining. It takes time, patience and several diamond drill bits. BTW the drill bits are not expensive. Around $10 HF gives a set of 10 or so of different sizes and shape. You need the pointy one to get started square at the center. This is the most important part of the drilling. The last thing you want to use is the bolt extractor! Once they are broke inside the hole, you are 10 times worse off than you started. Don't ask how I know!![]()