a fixing device for moulds for plastic articles , where a pair of half - moulds in which a force plug can be inserted , comprises at least one tie rod for keeping the two half - moulds in a closed position , the said tie rod being hinged , at one end , to the mobile half - mould and having a second end of a hammer - headed shape which hooks to two gripping jaws . the tie rod is hinged to a connecting rod which rotates on a pivot fixed to the resting base , which , in the movement of rotation , sets the tie rod along the line corresponding to the centroid of the pressure forces produced during the moulding operation .