HC49 Resistance Weld Crystals Fox / Abracon HC49 Resistance Weld Crystals feature a frequency tolerance of ±30PPM, frequency stability of ±50PPM, and an operating temperature range of -20°C to +70°C. The HC49 crystals are available with options for tolerances to 10PPM, frequency stabilities to 5PPM, and operating temperatures of -40°C to +105°C. The Fox / Abracon HC49 Resistance Weld Crystals' maximum height is 3.2mm.