Abstract: An x-ray tube rotor structure wherein a target support stem has an externally threaded end portion engaged with an internally threaded surface of an encircling bushing and fixedly attached thereto by an interposed brazed joint. The stem is made of predominantly molybdenum material having a linear thermal expansion coefficient of 58.times.10.sup.-7 per degree Fahrenheit and is thermally matched with the bushing which is made of an iron cobalt nickel alloy material having a linear thermal expansion coefficient of 60.times.10.sup.-7 per degree Fahrenheit. The bushing has an outer surface fixedly attached through a welded joint with an inner surface of an annular plug which has an outer marginal portion fixedly attached to an adjacent end portion of a coaxial rotor skirt. The annular plug is made of an iron chrome nickel alloy material having a linear thermal expansion coefficient of 84.times.10.sup.