Alloy 42 is a 41% nickel-iron controlled expansion alloy which has been used in a wide variety of glass-to-metal sealing applications.

While the expansion properties of this alloy most closely match 1075 glass, it has also been used in seals for the 0120 and 0010 glasses. It may also be used with hard glasses if a thin edged tubular seal is used. For seals that are not hydrogen annealed prior to sealing, a variation of this alloy containing small additions fo titanium, Glass Sealing 42 Gas-Free, has been used to promote gas-free sealing characteristics. Alloy 42 has been used for the glass-to-metal seals in electronic tubes, automotive and industrial lamps, transformer and capacitor bushings and other glass-to-metal and ceramic-to-metal applications.