This part is a kind of semiconductor called 1N5351B.

Function of this product has 5 WATT ZENER REGULATOR DIODES 3.3-200 VOLTS.

Manufacturers : Motorola Inc

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Some of the text within the PDF file :

MOTOROLA SEMICONDUCTOR TECHNICAL DATA 5 Watt Surmetic 40 Silicon Zener Diodes This is a complete series of 5 Watt Zener Diodes with tight limits and better operating characteristics that reflect the superior capabilities of silicon-oxide-passivated junctions. All this is in an axial-lead, transfer-molded plastic package that offers protection in all common environmental conditions. Specification Features: • Up to 180 Watt Surge Rating @ 8.3 ms • Maximum Limits Guaranteed on Seven Electrical Parameters Mechanical Characteristics: CASE: Void-free, transfer-molded, thermosetting plastic FINISH: All external surfaces are corrosion resistant and leads are readily solderable POLARITY: Cathode indicated by color band. When operated in zener mode, cathode will be positive with respect to ano [ ... ]

1N5351B PDF Datasheet Download