Here's its Item description: "An extremely valuable magic item on its own, the Gauntlet of Valor is part of one of only three remaining Power Arms made by the elven archmages of Myth Drannor. The devices were crafted for use by champions defending the ancient elven city on the rare occasions when it was in danger. This eternally shining gauntlet represents a pinnacle of elven craftmanship and enchantment. Adventurers and ambitious villians across the Realms yearn to find the location of all the pieces of the Power Arms.
Equipped abilities: -Immunity to Charm, Hold, Sleep and related spells
Combat abilities: -12% of all hits cause 3d6 points of crushing damage and stun the target for 3 seconds
Charge abilities: -Wearer can invoke the innate powers of the Gauntlet of Valor three times per day to be used as a weapon.
Based on that, I would think that 1/9 hits would do an extra 3-18 damage and stun ... which sounds awesome on top of regular damage. I have never seen it work - it's possible that it only works when the Charge ability is used, but it doesn't seem to indicate that in the text.