﴿ إِنَّا جَعَلْنَا فِىٓ أَعْنَٰقِهِمْ أَغْلَٰلًۭا فَهِىَ إِلَى ٱلْأَذْقَانِ فَهُم مُّقْمَحُونَ ﴾

“Behold, around their necks We have put shack­les, reaching up to their chins, so that their heads are forced up;”

(Lo! we have put on their necks) and hands (carcans) of iron (reaching unto the chins, so that they are made stiff necked) it is also said that this means: We pulled their hands to their chins when they were about to stone the Prophet (pbuh) while he was praying. Therefore, they are chained and prevented from all good.