Ael crystals hc 49u quartz crystal resonators through hole ael x4m000000l166 a 4000000mhz crystal resonator with a tolerance of 30ppm 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 x4m000000l166 40mhz 30ppm hc49u quartz crystal resonator