then the iron, the clay, the bronze, the silver, and the gold, all together were broken in pieces, and became like the chaff of the summer threshing floors; and the wind carried them away, so that not a trace of them could be found. But the stone that struck the image became a great mountain and filled the whole earth.
5
Then was the iron, the clay, the brass, the silver, and the gold broken to pieces together, and became like the chaff of the summer threshin…

Like the chaff — This language recalls Psalm 1:4; Psalms 2:9. It is emblematic of Divine judgments, as seen in Isaiah 4…

Although Daniel here records the dream and does not touch on its interpretation, yet we must not proceed further without discussing the matter itse…

Then was the iron, the clay, the brass, the silver, and the
gold, broken to pieces together

This image represented the kingdoms of the earth that would successively rule the nations and influence the affairs of the Jewish church.
Albert Barnes
AlbertBarnes