Hi Mink, That's an interesting question you have posted...Are you talking about a specific bushing to bore or pin to hole fit on the machine? I have never heard of a 3 thou per inch interference before...not to say that there isn't. A thou per inch is a good rule of thumb for a class 8 "heavy force" or "shrink fit". I would think that 3 thou an inch is beyond the elastic limits of any ferrous metal, especially cast iron. I would like to hear more on this too.
Regards, Bob