Alexander Dyce, A General Glossary to Shakespeare's Works

cracked “within the ring,” HAMLET, ii. 2. 423. “The gold coin of our ancestors was very thin, and therefore liable to crack. It still, however, continued passable until the crack extended beyond the ring, that is, beyond the inmost round which circumscribed the inscription; when it became uncurrent, and might be legally refused.” Gifford's note on Johnson's Works, vol. vi. p. 76. Hamlet alludes to the voice of the boy, who played female characters, becoming“cracked,” or too manly for those characters.