The ECS-40-20-4VX from ECS Inc. International is a RF Quartz Crystal with Frequency 4 MHz, Frequency Stability ±50 ppm, Frequency Tolerance ±30 ppm, Load Capacitance 20 pF, Equivalent Series Resistance 150. Tags: Thru Hole. More details for ECS-40-20-4VX can be seen below.