..or perhaps the threshold strip is for the bottom and the weatherstrip is for the top? My garage door has a strip at the top to stop wind and rain ingress.
I used two standard, screw-on door seals inside the bottom edge and they were cut to length. Cut the brush inserts to a slightly different length from the holders to avoid a gap. A 1" L-shaped plastic section neatly finished the top edge. One leg is hidden by the door. Total cost <£20.