If you need to lower your toolbox height so it will fit under a shelf or workbench, you can do it as long as you’re willing to empty and disassemble the toolbox.
Most toolboxes don’t have adjustable casters. But you can swap the casters under your toolbox for smaller ones to gain an inch of clearance, or possibly even two inches.
Casters are the key
Casters come in a number of sizes. Measure the wheels on the casters on your box, then visit your local hardware store or home center. If you buy shorter casters than the ones you have, you can lower the box. You’ll probably find emptying the toolbox is the hardest part of the job.
You can expect to pay around $25 for a new set of casters. Get two that swivel and at least one that lock. Ideally you want two swiveling, locking casters for the front of the toolbox. You can use Harbor Freight coupons to save money if you have a local Harbor Freight. They may be a bit lower quality but if you won’t be moving the box around every day, they’ll be fine.
This probably goes without saying, but we all make mistakes from time to time. Make sure all four casters you buy are the same size.
Swapping casters to lower your toolbox
Turn the box on its back or its side. You’ll either find four sets of nuts and bolts securing each caster to the box, or possibly just a single nut and a threaded connector on the caster. Remove the nuts and bolts as appropriate for your box, then swap in your new casters one at a time using the same nuts and bolts. Be sure to put your locking casters in front so you can lock the toolbox in place.
If the holes don’t line up, secure the caster with at least one, of the holes. Line the caster up square with the front ans side of the box, then drill new holes in the bottom of your toolbox to fit. To make it easier, drill a small pilot hole in the center then drill a bigger hole to fit the bolt. Be careful not to cut yourself on the burrs while securing the nut and bolt.
Set the toolbox upright and replace the bottom drawer. Fill the box back up and put it in place, and you’re done.