Lock the empty drawers of the tool box, and secure the drop-panels in the closed position. Protect the finish from scratches by placing carpet or packing from the carton the box came in on the ground for the box to rest on when it's inverted. Stand the box on its top.
Lay the caster angle plates in place across the bottom of the cabinet. Position the angle flanges face-up with the angles inboard, facing one another. Check the hole alignment through the angle plates to ensure proper placement.
Place the casters in position on the angle plates, with both swiveling casters on the same end of the cabinet, above the handle. Push the provided screws through the caster base and angle plates and tighten them. Return the box to the upright position.