Portable tread-plate toolboxes for storing and hauling tools on a truck bed, trailer, job site, or shop floor. These are diamond-plate boxes built to take abuse, gasketed lids, secure latching, and a footprint sized to fit standard mounting locations, not the tackle-box style storage you'd find at a hardware store.
The other half of this category is caster kits built specifically to mount under a toolbox and convert it from a stationary or truck-mounted box into a rolling one. They come in multiple wheel sizes and duty ratings, matched to how much weight the box and its contents will actually put on the wheels.