and width of the projecting part 8 is so selected that it at least extends over all of the pins 6 in the embodiment of the mold 4 shown in fig1 the width of the projecting part 8 corresponds to the width of the finished brush head 2 during injection of the plastic material only the mold cavity 5 of the mold 4 is filled and the body of the brush is manufactured the body comprises the brush head 2 and the brush neck 3 at that the wall thickness of the brush head 2 constitutes only a portion of the final thickness of the brush head 2 and is determined by the projecting portion 8 in the part 4a the pins 6 form in the brush head through openings 11 for receiving the bristle bundles the brush openings 11 are provided on the back side of the brush head 2 with chamfers 12 which are formed by bosses 10 of the projecting portion 8 of the mold part 4a naturally it is also possible to round off the active ends of the separate bristle bundles by grinding or the like this rounding off is effected in case when the bristle bundle is shaped.