Galvanizing, zinc, cadmium are all sacrificial coatings and will disappear over time. I wouldn't worry about the inside of a plated nipple as the entire block and heads coolant passages are bare cast iron and would rust long before the nipples will. I had these tools from a bathroom remodeling and they came in handy pulling a galled heater nipple on my 383 water pump. Had to use oxy/acetilene torch also. They got the job done asap and also on reinstallation of the new nipple. Would I buy a set to install a nipple? Probably not. Just an option put out to solve someone elses problem.