Abstract: A system for fastening an accessory (102) to a metal frame for doors, windows, or the like comprising at least one metal profile (110), including at least two parallel walls (112, 114, 116, 118). At least one of the walls (112, 114, 116, 118) has an outer surface (119) whereon the accessory (102)is fastened. The fastening system moreover comprises at least one self-threading fastening screw (126, 226, 326) including a manoeuvring head (128) and a threaded stem (136), whereon a main thread (144) engaging in coaxial through holes (120, 122, 124) on the parallel walls (112, 114, 116) winds. The threaded stem (136) comprises an initial stretch (138, 238, 338), adjacent to the manoeuvring head (128) and whereon the main thread (144) shaped for increasing the engagement surface between the threaded stem (136) and the wall (112) carrying the accessory (102) winds.