position the power head against the brush cutter housing in such a way that the support on the power head and the bearing housing at the curved end of the drive tube are pointing in the same direction. then align the power head and brush cutter so that the four holes line up. now slip the lock washers and plain washers onto the m6x20 hex. head screws. insert the screws and use a 10 mm open-end wrench to tighten them down securely in an alternate pattern.