Boys of the “twice-born” castes are initiated into the tradition in ceremonies called upanayana, which mark the beginning of formal instruction in sacred learning. The initiate receives a thread and wears it draped across the shoulder as a symbol of this “second birth.” Women no longer receive the thread and only Brahmins nowadays wear it when not engaged in ritual ceremonies. Sacred threads are of white wool for Brahmins, of red hemp for Kshatriyas, and of yellow wool for Vaishyas. Tradition dictated that Brahmins be initiated at seven or eight years of age, Kshatriyas at eleven, and Vaishyas at twelve. But regardless of caste, most of those who still engage in the formal ceremony generally associate it with puberty.