From DDO wiki
Effect: While this item is equipped, enemies you attack will be treated as having less Fortification than they actually possess.
- Named items
- Cannith Crafting: up to +23%
- Silent Avenger set: +5% heroic / 25% legendary (Artifact bonus to Armor-Piercing)
- Slave Lords Crafting: +8% / +28%
- Thunder-Forged crafting: Dragon's Edge +35%
- These stack with bonuses granted by any relevant feats such as Opportunist.
- These effects will apply to both equipped weapons when dual wielding.