Since the centers of these circles are connected through line segments they have the same radius, in this case, the segment HA goes from the center of the circle on the left to the bound of the circle, then its length is the radius of the circle, the same happens with the two segments BD anf BF, that go from the center of the circle on the right to the bound of the circle, as mentioned all the circles have the same radius, then HA, BD and BF are congruent.