Oops! Those screws are not normally welded to the shaft but they do have a blob of weld on the tip of the screws to prevent them from backing all the way out. The screws are not hardened,you may still be able to drill through them and run them on through with a square extractor. The drill bit may bite and run them on through while drilling. The screws are #6-40 oval head. Drive type doesn't matter.I did a bad thing. I removed the butterflies withe the hopes of cleaning/restoring not realizing the screws were welded to the shaft. Snapped them off and no way to replace.