We know from the Manusmriti that the first three Varnas (Brahmanas, Kshatriyas, and Vaishyas) are obligated to wear the Yajnopavitam.
Nowadays, it seems only Brahmins wear the thread and so it's even referred to as the "Brahmin thread".
So I'm wondering, are there any Kshatriya or Vaishya communities today who still wear it?