Zener voltage and power derating
The 1N6031B is a 200 V Zener diode in a DO-35 axial-lead package, rated for 500 mW continuous power dissipation. The ±5% tolerance on Vz means the actual breakdown voltage at the specified test current falls between 190 V and 210 V — tight enough for a rail clamp or reference bias in a discrete regulator.
Temperature grade and leakage
Reverse leakage is 100 nA maximum at 152 V, which is low enough to avoid loading a high-impedance bias node in a precision divider.