Giant Sword Sheath (5e Equipment)
From D&D Wiki
Weight: 1 lb.
This is a sword sheath, used to protect the blade of bigger swords like greatswords and similar weapons from oxidation and dirt. It is usually made of some flexible material, such as leather and hide. It contains a belt, for tying the sheathe on the back or waist, and a strap to prevent the sword from falling from it.
If you make an attack with a sheathed sword, the damage die decreases in one size (2d6 become 1d10, for example), and the damage type changes for bludgeoning. If the weapon have any magical bonuses to attack and damage, these doesn't apply to the damage of this attack.