Summary

I used the Gridfinity customizer over at https://gridfinitygenerator.com/ to generate the closest size base for the toolbox sections, then I edited the file to create the perfect fit in the lid and drawers. This is for the Mini Toolbox made by US General and sold at Harbor Freight stores. https://www.harborfreight.com/mini-steel-toolbox-black-72431.html They go on sale or have coupons that apply to this so the cost is well under $20.
Notes: In the drawers there is a magnet at the rear, and it protrudes about 6mm. This won’t impact the base, but it will prevent you from using the grid at the rear center. You can just leave it and not use that space, or you can cut it out and just glue the magnet in place. Additionally, these only fit the US General version. The very similar toolbox at Lowes under the brand Kobalt has slightly different dimensions. I’ll put one of those out to eventually and link it here when I do.

Details: Materials & Tools
• 3D Printing Filament: I used PLA, but PETG may be better if this is used in a hot garage.
• No Supports required
• No additional tools or parts needed
• Easy print just make sure you have good bed adhesion to prevent warping or elephants foot issues. On the Creality K1 Max with a textured bed that just means put down a fresh layer of glue stick. Other printers may be different.

Assembly
• Once printed you can optionally use magnets in the base, just make sure your polarity matches and is the opposite of the containers you choose to use.
• Putting in the base may be a tight fit but once you push it past the rivets it works well.
References:
• https://gridfinity.xyz/ by Zack Freedman – Thanks Zack for sharing this with us.
• https://gridfinitygenerator.com/
Final Notes
You don’t have to use this design and if you just go to https://gridfinitygenerator.com/ and export the base you want, it will work. It just won’t fit as snug and may move around on you a little bit. If this was helpful and you want to reward my work feel free to buy me a coffee at coff.ee/Jeramy. But don’t feel obligated, I’m not skilled enough at this to quit my day job anytime soon. Have a great day and enjoy making.