The Three-Wheeled Manual Wheelbarrow Retrofit Kit Retrofit Kit is designed to allow one to convert any wooden-handled, one-wheeled barrow into a three-wheeler. The pre-assembled kit includes brake, two wheels, undercarriage, handle, all required hardware, and retrofit instructions. A three-wheeled barrow is designed to eliminate tip-over and having to lift in order to move, and it reportedly pushes and dumps easily and minimizes the chances of back strain.