The ECS-40-20-4XDN from ECS Inc. International is a RF Quartz Crystal with Frequency 4 MHz, Frequency Stability ±100 ppm, Frequency Tolerance ±30 ppm, Load Capacitance 20 pF, Equivalent Series Resistance 150. Tags: Thru Hole. More details for ECS-40-20-4XDN can be seen below.