apparently no one has questioned the purpose of this metal colored ring according to google, and AI hallucinated an answer about corrosion resistance and how the plain black thread is nickel-plated metal even though it's plastic. it's literally just decorative from what i can tell.

https://www.neutrik.com/en/neutrik/products/plugs-jacks/jacks/m-series
>Fascia appearance can be black plastic or chrome.