I am doing a job for a friend on her water heater; the fitting for the emergency relief valve is busted (theives) off 'flush' with the threads. The ID opening is " 5/8 inch" & the extractor set I bought only has 1/8, 1/4, 3/8, 1/2, & 3/4... there is NO 5/8 extractor. How do I get the broken off fitting out... it is cast iron (or cast something). Thank you for your prompt answer.

