A "quartz crystal" is used in an oscillator circuit. They are used where an accurate frequency signal is required such as transmitter or calibration instrument. Your unit should also have a frequency printed on it.
Norm
: I have an old part called "quartz crystal" and the maker is Petersen Radio Co Inc
: and I began to think that this part is something to do with a radio, but
: I have no idea what for ..I s this quatz crystal can be use for a radio