If held by a Flying-type Pokémon, it takes damage from Ground-type moves as if Ground-type moves dealt 1× damage to pure Flying-type Pokémon.
Even if the holder has Klutz or is affected by Embargo, its Speed is still halved by the Iron Ball.
Generation V onward
If held by a Flying-type Pokémon, it takes 1× damage from Ground-type moves, regardless of its other types. This does not apply during Inverse Battles or if the holder is grounded by any other effect.