1500 W surge rating and the protection window it defines
The 1.5KE300AHA0G: Its 256 V reverse standoff voltage means the protected rail can sit at that DC level without the diode conducting leakage current, while the minimum breakdown of 285 V and maximum clamping of 414 V at 3.8 A define the window where the diode absorbs the transient.
Automotive-grade thermal and reliability envelope
The DO-201AA axial package (DO-27 equivalent) is a through-hole form factor that handles the thermal cycling of power-train and body-control modules without the solder-joint fatigue risk of a surface-mount part in the same temperature swing.