The ECS-40-18-5PXEN-TR from ECS Inc. International is a RF Quartz Crystal with Frequency 4 MHz, Frequency Stability ±50 ppm, Frequency Tolerance ±30 ppm, Load Capacitance 18 pF, Equivalent Series Resistance 150. Tags: Surface Mount. More details for ECS-40-18-5PXEN-TR can be seen below.