1) Men wearing silver rings are limited to 4.86g & Sterling Silver is 92% pure silver, so is it permissible for men to wear such rings?
2) Can men wear other jewellery like necklaces and watches?
In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
1) Firstly, the purity of the silver in the ring and the weight of the ring are two completely different matters. In principle, men are permitted to wear only silver rings or rings which are plated with silver , with the condition that they are limited to 4.86g (excluding stone). The head of the ring may be from any type of stone (eg. diamonds etc).
With regards to Sterling silver, it must be noted that this is an alloy created when copper is added to pure silver . As you indicate in your question, usually, sterling silver has a purity of 92.5%, meaning that 7.5% of the alloy is made of copper or another metal (usually nickel or zinc). As indicated by the name, the predominant metal in Sterling Silver is indeed Silver itself. Thus, it will be regarded as silver and it will be permissible for men to wear (if limited to 4.86g), as outlined above. 
2) Wearing a standard watch, for the purpose of keeping track of time, is perfectly fine. However, one should avoid gold watches, however, watches with diamonds etc are perfectly fine. Furthermore, men should avoid wearing necklaces and all other types of jewellery. As outlined above, the ring is an exception, because it is established that Rasulullah ﷺ possessed and wore a silver ring. Thus, despite the discussion of whether it is better for the man to use a ring or avoid it, it is permissible nonetheless.
And Allah Ta’āla Knows Best.
Mufti Mubasshir Talha
10 Dhul-Qa’dah 1441 / 1 July 2020
Mufti Tahir Wadee | Mufti Yusuf Ilolvi
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ولا يتختّم إلا بالفضة
[Jami’ Al-Saghir, 232, Ibn Hazm]
ومنها: الفضة لأن النص الوارد بتحريم الذهب على الرجال يكون واردا بتحريم الفضة دلالة فيكره للرجال استعمالها في جميع ما يكره استعمال الذهب فيه إلا التختم به
[Al-Badai’ al-Sana’i, 6.526, DKI]
[Al-Bahr al-Ra’iq, 8/349, DKI]
وأما التختم بما سوى الذهب والفضة من الحديد والنحاس والصفر فمكروه للرجال والنساء .جميع
[Al-Badai’ al-Sana’i, 6.526, DKI]
فعلم أن التختم بالذهب والحديد والصفر حرام
[Radd al-Muhtar, 6/359, HM Saeed]
وغالب الفضة والذهب فضة وذهب
[Al-Durr al-Mukhtar, 5/553, HM Saeed]
لا بأس بأن يتخذ خاتم حديد قد سوي عليه فضة وألبس بفضة حتى لا يرى
[Radd al-Muhtar, 6/360, HM Saeed]
ولا يزيد وزنه على مثقال لقوله – عليه الصلاة والسلام – «اتخذه من ورق ولا تزده على مثقال»
[Al-Bahr al-Ra’iq, 8/340, DKI]
وينبغي أن يكون قدر فضة الخاتم المثقال ولا يزاد عليه، وقيل: لا يبلغ به المثقال
[Muhit al-Burhani, 5/349, DKI]
مرد کو صرف چاندی کی انگشتری کی اجازت ہے وہ بھی ایک مثقال سے کم
[Fatawa Mahmudiyyah, 19/339, Jamiah Faruqiyyah]
مرد کے لۓ دو شرطوں سے انگھوٹھی پہننا جائز ہے۔
۱) چاندی کی ہو
۲) پانچ ماشے = 4.82 گرام سے کم ہو
[Ahsan al-Fatawa, 8/69, HM Saeed]