What does the cryptic crossword clue "They may be spun – to make briefs? (6)" mean?

The definition is "They may be spun". The wordplay uses an anagram. anagram of BRIEFS? = FIBRES; definition: "They may be spun" The answer is Fibres.

They may be spun – to make briefs? (6)

Telegraph #27738 | 12 Across | 2015-03-02 flower