Part of the Dreadnaught's Battlegear set:

The set gives these bonuses as more pieces are worn: 2: Increases the damage done by your Revenge ability by 75. 4: Improves your chance to hit with Taunt and Challenging Shout by 5%. 6: Improves your chance to hit with Sunder Armor, Heroic Strike, Revenge, and Shield Slam by 5%. 8: When your health drops below 20%, for the next 5 seconds healing spells cast on you help you to Cheat Death, increasing healing done by up to 160. Set Details | All Sets

Disenchants into

Name	Value	Drop%
Nexus Crystal	1 Copper	100.0%