This is just what I need to ream a few holes in 12" x 12". The ship's drill chisel became tangled in the existing hole. The idea was to make some sort of pilot hole for this that would be deep enough so the drill wouldn't chew through the surface of the hole. It did just that. For holes that widened from 1/2 inch to 1 inch, a marine screw (Irwin) was centered to widen the holes. When expanded from 3/4" to 1" it didn't quite center, but it didn't deviate much either (the old hole was expanded and the new hole wasn't drilled). This took quite a bit of effort and the shank is somewhere between 1/4" and 1/2" so it didn't fit any of my extensions (I was hoping to put it on a long extension and slide it lower. If you try this, I'm not sure if the hole stays straight, I have a longer extension that I could use to push it all the way through.)