Your Saw Blade Guard is the original version of that set P/N 505875 that had only a 1-1/4" dust collection connection. It was upgraded and the tie bar shield you show is only part of the upgrade to two 2-1/2" dust collection ports. The first picture below shows the original Saw Blade Guard set. The second picture is the upgrade. Note the upper Blade Guard remained the same.
Without the complete upgrade package the part that attaches to the tie bar doesn't work well with the old lower part of the original guard.
