The Belt of Primus was a powerful artifact. Its origin is not exactly known, but it bears the symbol of the Modron leader, Primus.
When worn, the belt makes the wearers skin as hard as adamantine, making any critical hit against you become a normal hit and bludgeoning, piercing, and slashing damage that you take from non magical weapons is reduced by 3.
The only known wearer of this kind of belt was the dwarf, Dirk Dankil. It is unknown if there are any others.