The grass cutting head (1) comprises a housing (3), inside which a spool (11) is provided to wind the cutting line (F). The housing has holes (9) for the passage of the cutting line (F) towards the outside of the housing. The spool (11) has at least a flange (15) with openings (31) allowing to insert the cutting line (F) into a passage defined between the flange (15) and a transverse wall (3B) of the housing.