It's a bracket that allows the cutter to float better.
Let's say, you go across a ditch, by the time your rear wheels are on the bottom of the ditch, the tail wheel of the cutter tries to "lift" the cutter and push on the top link. With this bracket, it allows for a little bit of movement which then allows the cutter to follow the ground better.
Here is a picture. Note the bracket on the top link:
Manufactures should really just use chains between the top link A frame and the rear of the cutter instead of these flimsy bars but that's another subject.