They're used for cutting bits of grass (6)
I believe the answer is:
blades
'bits of grass' is the definition.
(I've seen this in another clue)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for blades that I've seen before include "Football club nickname" , "Cutting parts of knives" , "They cut" , "Knife edges or dashing fellows" , "Leaves of grass or cutting tools" .)