Rock blasters (4)
I believe the answer is:
amps
'rock blasters' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for amps that I've seen before include "Current measures" , "Spam (anag)" , "Units of electrical power" , "'Units of electric current, in short (4)'" , "Basic units of electric current" .)