I don't know the reason for the cross bar having a rod end. The left to right side can twist meaning if, for example, you went into a corner and the left side mount is attempting to move in an arc due to the twisting of the k-frame about the axis going front-rear in the car Since there is a ball there, it just keeps the straight line distance to the other side the same only in the cross car direction, it will do zero for any simultaneous front-back movement because it will just pivot on the rod end instead of having to bend the rod to deflect. With only one bolt on each side, it can also run an arc. The degrees of freedom are not adequately restricted to get the best possible effect. For example, my truck has a removable crossmember similar to the transmission crossmember on our cars in roughly the same area and it has two bolts on each side with what's essentially a box tube in the middle. It has no degrees of freedom other than literally twisting the steel.