Hard sand used by manual workers (5)
I believe the answer is:
hands
'manual workers' is the definition.
(eg factory hands)
'hard sand used by' is the wordplay.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'used' indicates an anagram.
'by' means one lot of letters go next to another.
'sand' is an anagram of 'ands'.
'h'+'ands'='HANDS'
(Other definitions for hands that I've seen before include "Measurements for horses" , "Cards given out in deal" , "Workers" , "Those holding harness" , "Units for measuring horse's height" .)