Nasai

(1) The purpose of the chapter heading established by Imam al-Nasa’i rahimahullah is to clarify this important issue: that it is legally permissible (shar‘an) to wear an iron ring that has a silver covering. It is necessary to avoid wearing a ring made purely of iron, because it has been described as the adornment of the people of Hell. (: al-Mawsu‘ah al-Hadithiyyah, Musnad Ahmad: 11/69).

(2) This blessed hadith also proves that serving the people of knowledge and virtue is recommended (mustahabb). Furthermore, it is permissible to have a free man perform service as well, provided that he is willing and consents to do so gladly.

(3) It is necessary to safeguard official seals, as well as those of other important institutions, which are used to stamp letters and documents, so that they are not misused by anyone. Otherwise, all such documents and letters would be rendered invalid and unreliable. And Allah knows best.

Benefits and Issues:
The material with which an iron ring is plated will take the same ruling as that material, whether it is gold or silver.
And for men, silver is permissible.
And Allah knows best.

Explanation:
1:
This refers to "Abdur Rahman," the son of Abu Rafi‘ radi Allahu anhu, who was the freed slave of the Messenger of Allah sallallahu alayhi wa sallam.

Note:
(Based on corroborating evidence, this hadith is sahih li ghayrihi (authentic due to supporting narrations); otherwise, its narrator "Abdur Rahman ibn Abi Rafi‘" is considered weak in hadith.)