Crystal Oscillator is a component that generates a clock pulse of a precise frequency. Crystal oscillator mostly consists of a quartz crystal. It generate a stable clock signal for the microcontroller. This particular Crystal is a genuine product from "Raltron Electronics Corporation" and has 16MHz frequency, the same that is default for the Arduino boards. It can used to isolate ATmega328 and similar chips for use in your custom PCBs. We have also included 2 20 pF ceramic capacitors that are always used along with the crystal.