Increases the attack speed of the Hero by 15% when worn.
Arthas can find one in Digging up the Dead, chapter 2 of the Warcraft III undead campaign, Path of the Damned.
Tyrande can find one in Daughters of the Moon, chapter 2 of the night elf campaign, Eternity's End.
Illidan can find one in A Destiny of Flame and Sorrow, chapter 6 of that campaign.
Kael and Lady Vashj can find one in The Crossing, the secret level of the Frozen Throne alliance campaign, Curse of the Blood Elves.