The ECS-40-20-28AX-TR 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 200. Tags: Surface Mount. More details for ECS-40-20-28AX-TR can be seen below.