I want to present an interesting fact on how the theme of the "rod of iron" appears in Scripture. It is a theme that first appears in Book 19, in the great Messianic prophecy of God's Son as King:

Psalm 2:9 Thou shalt break them with a rod of iron; thou shalt dash them in pieces like a potter's vessel.

So the first mention of Christ's Rod of Iron in Scripture is in Book 19, Chapter 2.

Where else does this theme appear in Scripture? In only one more book, Revelation:
Revelation 2:26 And he that overcometh, and keepeth my works unto the end, to him will I give power over the nations:
Revelation 2:27 And he shall rule them with a rod of iron; as the vessels of a potter shall they be broken to shivers: even as I received of my Father.
This verse is a direct quote of Psalm 2! There is therefore a link between Psalm 2 and Revelation 2. This has been documented in more detail in the article Rev 2 - The New Name, Rod of Iron.

Now I want to point out to something more. The "rod of iron" appears elsewhere in Revelation. You can find it in Revelation 19!
Revelation 19:15 And out of his mouth goeth a sharp sword, that with it he should smite the nations: and he shall rule them with a rod of iron: and he treadeth the winepress of the fierceness and wrath of Almighty God.
So the Rod of Iron that debuts in Book 19, Chapter 2 also appears in Revelation 2 and Revelation 19!

The Scriptural appearances of Christ's symbol of authority over the nations seem to be carefully allocated in Scripture! This sounds pretty much like the appearances of the theme of the potter's vessel being broken that is found in the same seminal context of Psalm 2:9. See the thread Jeremiah 19 and Psalm 2 (2:19 and 19:2).

But there is one more gem to share. The Rod of Iron appears a third time in Revelation, a mention that I deliberately skipped. The interesting thing is where it appears. If we measure the distance between the other two, Revelation 2:27 and 19:15, we'll find that the remaining occurrence appears in the almost exact center between these two verses! It is off by merely eight verses.
Revelation 12:5 And she brought forth a man child, who was to rule all nations with a rod of iron: and her child was caught up unto God, and to his throne.
So we have three occurences of "rod of iron" in Revelation and they appear once in Revelation 2, once Revelation 19 and once halfway through Revelation 2 and 19!

Their positions in the text seem to be by design of the Book's Author!