Ael crystals hc 49u quartz crystal resonators through hole ael x4m000000l167 a 4000000mhz crystal resonator with a tolerance of 20ppm in a hc 49u style holder that is suitable for a wide range of frequency control applications and serves as direct replacement for existing designs ael x4m000000l167 40mhz 20ppm hc49u quartz crystal resonator