In verse 38, it was said: مُقَرَّ‌نِينَ فِي الْأَصْفَادِ (held in chains). Details about the subjugation of Jinns and the services they performed have appeared earlier in the commentary on Surah Saba' within this Volume VII. Here, it has been said that Sayyidna Sulayman (علیہ السلام) was holding the unruly Jinns by having them chained. Now, it is not necessary that these chains be the visible chains of iron. It is possible that there could have been some other method used to tie them up more tightly or securely - and it has been expressed as 'chains' for the sake of common comprehension.