Iowa Code § 321.462: Drawbars and safety chains.

When one vehicle is towing or pulling another vehicle the drawbar or other connection shall be of sufficient strength to pull all weight towed thereby and shall be fastened to the frame of the towing vehicle in such manner as to prevent sidesway, and in addition to such principal connection there shall be a safety chain which shall be so fastened as to be capable of holding the towed vehicle should the principal connection for any reason fail.