The Rear Bumper Frame Kit is a required component is installing the frame brace. However these have also been engineered to reinforce the mounting surface of the rear cross member. They have been designed with enough provisions to install on the rear cross member, but to also accept the frame brace.
Even though most Jeeps have the same mounting provisions for a rear bumper, certain models are older and have weaker cross members that can benefit from reinforcement. The Rock Hard Rear Bumper Frame Kit can add more structural integrity to the rear cross member, and make for a stronger rear bumper if it should happen to come in contact with any elements found on the trail.