The BZM55C18 from Micro Commercial Components is a Zener Diode with Zener Voltage 16.8 to 19.1 V, Zener Current 1.0 mA, Voltage Forward 1.5 V, Current 5.0 mA, Current Reverse Reverse Leakage Current:- 0.1 - 2.0 uA. More details for BZM55C18 can be seen below.