Abstract: A heater assembly for mounting around a fluid flow channel in an injection molding apparatus, the heater assembly comprising: an inner tube comprising a first heat conductive material having a first coefficient of thermal expansion, the inner tube having a selected longitudinal length, an inner surface, an outer surface; a first ring having an inner surface engaged around the outer surface of the inner tube along short selected length of the longitudinal length of the inner tube, the first ring comprising a second material having a second coefficient of thermal expansion that is less than the first coefficient of thermal expansion; a heater mechanism that heats the inner tube to a selected elevated temperature.