Revelation 9:9

They had breastplates like breastplates of iron; and the sound of their wings was like the sound of chariots, of many horses rushing to battle.

Job 39:25

“As often as the trumpet sounds he says, ‘Aha!’
And he scents the battle from afar,
And the thunder of the captains and the war cry.

Job 40:18

“His bones are tubes of bronze;
His limbs are like bars of iron.

Job 41:23-30

“The folds of his flesh are joined together,
Firm on him and immovable.

Isaiah 9:5

For every boot of the booted warrior in the battle tumult,
And cloak rolled in blood, will be for burning, fuel for the fire.

Joel 2:5-8

With a noise as of chariots
They leap on the tops of the mountains,
Like the crackling of a flame of fire consuming the stubble,
Like a mighty people arranged for battle.

Nahum 2:4-5

The chariots race madly in the streets,
They rush wildly in the squares,
Their appearance is like torches,
They dash to and fro like lightning flashes.

Revelation 9:17

And this is how I saw in the vision the horses and those who sat on them: the riders had breastplates the color of fire and of hyacinth and of brimstone; and the heads of the horses are like the heads of lions; and out of their mouths proceed fire and smoke and brimstone.

Treasury of Scripture Knowledge

Summary

And they had breastplates, as it were breastplates of iron; and the sound of their wings was as the sound of chariots of many horses running to battle.

Bible References

They had

Revelation 9:17
And this is how I saw in the vision the horses and those who sat on them: the riders had breastplates the color of fire and of hyacinth and of brimstone; and the heads of the horses are like the heads of lions; and out of their mouths proceed fire and smoke and brimstone.
Job 40:18
“His bones are tubes of bronze;
His limbs are like bars of iron.
Job 41:23
“The folds of his flesh are joined together,
Firm on him and immovable.
Joel 2:8
They do not crowd each other,
They march everyone in his path;
When they burst through the defenses,
They do not break ranks.

And the

Job 39:25
“As often as the trumpet sounds he says, ‘Aha!’
And he scents the battle from afar,
And the thunder of the captains and the war cry.
Isaiah 9:5
For every boot of the booted warrior in the battle tumult,
And cloak rolled in blood, will be for burning, fuel for the fire.
Joel 2:5
With a noise as of chariots
They leap on the tops of the mountains,
Like the crackling of a flame of fire consuming the stubble,
Like a mighty people arranged for battle.
Nahum 2:4
The chariots race madly in the streets,
They rush wildly in the squares,
Their appearance is like torches,
They dash to and fro like lightning flashes.