I pre-drilled the broken bolt under the casting using a drill guide purchased from Revain. Using the drill guide I also inserted the left bit and to my surprise the broken part started to slide out again.
I have an Irwin Master Bolt Extractor Kit and I broke a 1/8" bit. They have a pack of 6 of these bits but it says 'delivery between 1 and 2 months' so I bought this as a backup plan. Irwin kit made chips easy. Don't waste your time with this brand.
I could not dent the stainless steel screw (approximately 3/16-1/4 inch) that I was attempting to remove. This propeller on my boat broke the head off. I tried to make a hole to insert the extractor with this drill bit. Couldn't do it after 30 minutes of trying. My mechanic was on the boat fixing the engine and he tried too. I used a Dewalt 3/8 20 volt drill bit. Maybe a more powerful drill? And the drill was in the opposite direction.