I was fortunate enough to score two of these neat little vintage toolboxes at an estate sale for $4 each! I was super excited to get them home. With my limited amount of space on my patio, I chose to stack them on top of each other. Eventually, they became very heavy and I started having problems when I needed to move them around my patio. The bottom wheels were not moving well with all the added weight and they would start tipping over so I decided to reinforce them and put larger wheels with ball-bearings in them to make it easier to move them around on my patio.
First I started with 1 1/2 by 1 1/2 inch piece of steel box iron a neighbor gave to me he had leftover from a tour bus he was stripping down. If I didn’t happen to have the box iron I could’ve used a couple of solid pieces of 2 x 4 wood. They also would have worked well with this project, be resourceful, and use what you got!
I emptied my toolboxes of all of their contents and get them on their back and do some measuring to see how much steel I needed to fit into the floor of each toolbox. Once this was done, I started drilling holes to mount them to the toolbox floors.
Once I got the 3/16th inch metal screws in and tightened down for each box ( these screws came with the box iron that I got from my neighbor) then the next step was to drill mounting holes with a 7/16th inch drill bit to mount the two boxes together. I used four 3/8ths inch bolt and nut combo and the bolt was about 3 inches long so it could make it through both boxes and the box iron with washers at both top and bottom of the bolt and nut. 
Now the next step is just adding the holes in the bottom toolbox so I can finally install my new heavy-duty wheels! Vintage renewed!!!! Now it rolls around like a dream. Ball-bearing wheels saved the day. 
