Tafsir of Ghafir 40:71

( Idh [when] the shackles are in their necks... ) Idh is an adverbial of time for "they shall know," and the meaning is directed toward the future. The use of the past tense verb is to indicate its certainty, as if it has already occurred in reality; thus, there is no contradiction between "will" (sawfa) and "when" (idh).

( And the chains ) is a conjunction linked to "the shackles." The prepositional phrase is conceptually placed at the end, as if it were said: "when the shackles and the chains are in their necks."

And His saying—Exalted is He—( they are dragged ) means they are hauled.