Block from U+3200 to U+32FF. This block was introduced in Unicode version 1.1 (1993). It contains 254 codepoints.
The Wikipedia provides the following information on block Enclosed CJK Letters and Months:
Enclosed CJK Letters and Months is a Unicode block containing circled and parenthesized Katakana, Hangul, and CJK ideographs. During the unification with ISO 10646 for version 1.1, the Japanese Industrial Standard Symbol was reassigned from the code point U+32FF at the end of the block to U+3004. Also included in the block are miscellaneous glyphs that would more likely fit in CJK Compatibility or Enclosed Alphanumerics: a few unit abbreviations, circled numbers from 21 to 50, and circled multiples of 10 from 10 to 80 enclosed in black squares (representing speed limit signs).