Hard toenails have broken hard bit of shower (9)
I believe the answer is:
'hard bit of shower' is the definition.
(hard bit of a hail shower)
'hard toenails have broken' is the wordplay.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'have broken' indicates an anagram.
'toenails' is an anagram of 'ailstone'.
(Other definitions for hailstone that I've seen before include "bit icy", "drop of ice", "sign of cold weather", "It lands with a noise", "a drop of the hard stuff?".)