This part is a kind of semiconductor called 1N5611.

Function of this product has Voidless Hermetically Sealed Unidirectional Transient Voltage Suppressors.

Manufacturers : Microsemi

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Some of the text within the PDF file :

1N5610 thru 1N5613 Available on commercial versions Voidless Hermetically Sealed Unidirectional Transient Voltage Suppressors Qualified per MIL-PRF-19500/434 DESCRIPTION This series of industry recognized voidless hermetically sealed unidirectional Transient Voltage Suppressor (TVS) designs is military qualified and are ideal for high-reliability applications where a failure cannot be tolerated. They provide a Working Peak “Standoff” Voltage selection from 30.5 to 175 volts with 1500 watt ratings. They are very robust in hardglass construction and also use an internal metallurgical bond identified as “Category 1” for high reliability applications. These devices are also available in a surface mount MELF package configuration as a special order. Microsemi also offers numerous ot [ ... ]

1N5611 PDF Datasheet Download