The 1N6004B is a 15 V Zener diode in the standard DO-35 glass axial package, rated 500 mW continuous power dissipation. The ±5% tolerance on the nominal Zener voltage means the regulation point sits between 14.25 V and 15.75 V at the specified test current — tight enough for a 15 V rail clamp or a reference in a low-power bias supply. The 32-Ohm maximum dynamic impedance (Zzt) at the Zener test point means the regulation voltage shifts about 32 mV per mA of load current change — a consideration if the diode is used as a shunt regulator rather than a simple clamp. Reverse leakage is specified at 100 nA maximum at 11 V reverse voltage, which is 4 V below the Zener knee — this confirms the diode is fully off below the regulation region, with negligible leakage in a voltage-clamp application where the rail stays below the Zener voltage.
Microchip Technology lists the 1N6004B as Obsolete. No pin-compatible direct replacement from Microchip is documented, so a BOM substitution would require a parametric match on voltage, tolerance, power, and package.