Kovar (traemark of Carpenter Technology Corporation) is a nickel-cobalt ferrous alloy designed to be compatible with the thermal expansion characteristics of borosilicate glass (~5×10-6 /K between 30 and 200°C, to ~10×10-6 /K at 800°C) in order to allow direct mechanical connections over a range of temperatures. It finds application in electroplated conductors entering glass envelopes of electronic parts such as vacuum tubes (valves), X-ray and Microwave tubes and some lightbulbs.