Find a steel frame, two-wheel hand dolly. An older model may need minor refurbishing so that it is in good working condition.
Measure the base of the dolly to determine the width of the sheet of metal that will attach to the base. Place the sheet of metal on the base of the dolly and mark the four corners where you will drill holes through the metal and the base.
Drill ¼-inch holes in the four corners of the base of the dolly and in the four corners of the sheet of metal using a power drill with a ¼-inch drill bit.
Lay the sheet of metal on top of the base of the dolly, lining up the holes you drilled. Slide screws down into each hole, securing them by slipping a washer, then a nut up the screw on the bottom of the dolly. Tighten the screw with a screwdriver while holding the washer with a wrench. If the ends of the screws protrude too far, cut them off with a hacksaw.
Bend the flexible metal tubing into the shape of a hook. Flatten and shape the hook’s end into a fine point with a hammer.
Drill a ½-inch hole in the handle at the top of the dolly and a ½-inch hole in the bottom of the metal tubing, perpendicular to the point of the hook.
Attach the metal hook to the handle of the dolly. Slide a bolt with a small spring on the end of it through the hole of the dolly and through the hole in the metal hook so that the end of the bolt points to the front of the dolly. Slide a washer, then a nut onto the bolt, snug against the spring. Adjust the tension of the hook by tightening or loosening the bolt. This hook will nestle into the hay bale as it is being transported and hold it in place.