KJV:
And the fourth kingdom shall be strong as iron: forasmuch as iron breaketh in pieces and subdueth all things: and as iron that breaketh all these, shall it break in pieces and bruise.
NASB:
"Then there will be a fourth kingdom as strong as iron; inasmuch as iron crushes and shatters all things, so, like iron that breaks in pieces, it will crush and break all these in pieces.