It clamps transients on a 69.2 V nominal rail to 125.1 V maximum, with a breakdown voltage of 86.5 V minimum. The single bidirectional channel means it handles both positive and negative surges on the same line, which simplifies layout for AC-coupled or floating signal lines. The axial through-hole package (B, Axial) is a legacy footprint — expect manual insertion or wave-solder assembly, not reflow.
Temperature range and thermal reality
At 175°C the leakage current through the Zener junction rises significantly — derate the peak pulse power per the datasheet curve above 25°C. In a 125°C ambient, the 500 W rating drops to roughly 250 W; plan the surge budget accordingly.
The base product number is 1N6129, and the 'A' suffix indicates a tighter tolerance on breakdown voltage.