Related: Best Modular Tool Storage Systems for a Home Shop
A modular tool storage system is only worth the money if it makes putting tools away easier than leaving them on the bench. That's the whole test. I'm a diesel mechanic, 16 years in, and my home shop started with one toolbox and metastasized into three, plus a wall of organizers my wife calls the plastic wall. Everything in this guide earns its footprint, or it doesn't come home with me.
Here's what nobody tells you when you're shopping: you're not really buying a box, you're buying a place for every tool. The box is the easy part. The small parts are what kill you. The 10mm sockets, the fender washers, the roll pins, the O-rings that seem to reproduce in the dark. An apprentice I worked with lost three 10mm sockets in one week, and that's what made me rethink drawer layout from the dividers up.
So I split storage into two jobs. The stuff that has to travel with you, and the stuff that has to sit still and stay sorted. Get both right and you stop losing tools. Get one wrong and you'll be digging through a bucket with a flashlight in your teeth at 6:40 in the morning while the foreman watches.
Everything below is a real product I'd put in a real shop, ranked by the job it does. Two of them are mobile systems, two are organizers for the little stuff, and all four answer the same question: does this make putting the tool back easier than leaving it out?
Best Overall: Milwaukee Packout Rolling Modular Stackable Tool Box Storage System, Red
The Packout is the best modular system I've used, and the rolling base is the reason to start here. A stack is only as good as the thing at the bottom of it, and putting the wheels on the largest unit means you move the whole stack instead of unloading it. The cases lock together, so the stack stays a stack when you roll it across a shop floor with a seam in the concrete. That sounds like a small thing until you've watched a tower of boxes walk itself apart while you push it.
The drawers lock tight, and it stacks like LEGO for adults. That's not a cute comparison, it's the actual experience: you commit to the footprint once, then every case you add has a home and a locking point. For a mechanic who moves between a garage, a driveway, and a buddy's house on a Saturday, that's the difference between a job and a hauling exercise.
The trade-off is that it's a system, which means the first purchase is the cheap part. Once you're in, you keep buying modules, and the stack grows until you have to think about where it lives. It's also not light once it's loaded. Roll it, don't lift it into a truck bed unless you like your spine the way it is.
Check the casters when it shows up. On a loaded box, locking casters are non-negotiable, and a caster that only locks on one wheel is worse than no lock at all, because it gives you false confidence on a sloped driveway. 
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Best for Fasteners: CASOMAN Tool Box Organizer Interlocking 2-Piece Pack
The CASOMAN organizers are the ones I'd hand to somebody whose fasteners are currently living in a coffee can. Two pieces, interlocking, with removable dividers, and the dividers are the detail that matters most. Fixed compartments are a compromise somebody else made on your behalf. Removable dividers let you size the bays to the parts you actually own: a wide bay for the 3/8 washers, narrow slots for roll pins, one big compartment for the mystery hardware that comes with every job and never goes back where it came from.
Interlocking means the two units lock to each other, so they stay put as a pair instead of sliding around on a shelf or shifting in a drawer every time you open it. Black is the right color for shop hardware, because it hides the grease that will absolutely end up on them.
What it isn't: this is not the box you drop a socket set into. It's for small parts, fasteners, and crafts, exactly as the label says, and it does that one job well. If your hardware situation is worse than you think it is, and it is, buy two packs and sort by class from day one. 
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Best Carry Box: Jack Boss 16-Inch Steel Tool Box
Every shop needs one traditional box you can grab with one hand and carry to the job. That's what this Jack Boss is. Steel body, aluminum alloy handle, double lock, and a removable tray. The tray is the part that makes it useful, because it gives you a top layer for the tools you touch on every job and a bottom cavity for everything else. Ratchet, extensions, a couple of wrenches up top. The rest of the world underneath.
The double lock is two latches, and on a box this size that's the difference between a lid that stays shut when you set it down hard and a lid that pops open and introduces your sockets to the gravel. The aluminum handle is the part you'll notice when the box is loaded, because a steel handle on a full box digs into your hand on the walk from the truck to the job.
Where it goes: on a service cart, on a shelf by the door, or in the trunk as the road box. Sixteen inches is a size you can carry loaded without hating your life, which is more than I can say for the big chests. If you want one box that does a job start to finish, this is the shape to buy. 
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Best Value Small Parts Storage: CRAFTSMAN Storage Organizer 3-Pack
Three organizers, 10 compartments each, lid with a secure latch. The 3-pack is the value play, and the reason is simple: three boxes let you sort by class instead of by pile. One for metric hardware, one for standard, one for electrical connectors and crimps. Once you've done that, you stop digging and start grabbing, and grabbing is the whole point of owning storage.
Ten compartments per box is enough to separate without getting fussy. I've used organizers with so many tiny bins that sorting took longer than the repair, and I've used boxes with four giant cavities that turned into a junk drawer with a handle. Ten is the middle that works.
The latch on the lid is the thing to check on any organizer, and this one is called out as secure for a reason. A latch that pops when you carry the box by the lid will dump your sorted hardware on the driveway, and then you get to sort it twice. 
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How I judge tool storage in a working shop
Open the drawer. Feel the slide. That's the whole review. Everything else is marketing.
The slides. Ball bearings or you're buying a metal box with a label. Friction slides are fine for the first year and a punishment after that, because by year two you're pulling drawers with both hands and a hip. If a box advertises friction slides, keep walking.
The put-away test. The best storage is the kind that makes putting tools away easier than leaving them out. If the drawer is stiff, or the compartment doesn't fit the tool, or the latch needs two hands, the tools end up on the bench. A messy bench isn't a discipline problem, it's a storage design problem.
The carry test. Pick it up by the handle or the lid, loaded, and walk 30 feet. Anything that flexes, rattles, or digs into your fingers fails. That's why the removable tray and the aluminum handle on the Jack Boss matter more than the paint.
The caster test. On anything with wheels, roll it over a floor seam and lock it. A loaded box that rolls and locks properly is worth every dollar of the premium, and one that only locks on a single wheel is a liability on any slope.
The weight-rating caveat. Weight ratings on tool chests are measured with the load spread evenly. A drawer full of sockets is not even. So I don't trust the number on the spec sheet, I trust how the box behaves when the load is where the load actually goes, which is all in one corner.
The comparison table
This is how the four stack up against each other by job. Prices move, so check the current listing rather than trusting anything you read in a chart, including mine.
| Product | What it is | Best for | Where it belongs | Price |
|---|---|---|---|---|
| Visit on Amazon → Milwaukee Packout Rolling Modular Stackable Tool Box Storage System |
Rolling modular stackable system | Moving a whole job between locations | Bottom of the stack, by the shop door | Visit on Amazon → |
| Visit on Amazon → CASOMAN Tool Box Organizer Interlocking 2-Piece Pack |
Interlocking organizer with removable dividers | Fasteners and small parts you sort by size | Bench shelf or inside a drawer | $21.57 |
| Visit on Amazon → Jack Boss 16-Inch Steel Tool Box |
Steel carry box, aluminum handle, double lock, removable tray | One job start to finish | Service cart or truck trunk | $39.99 |
| Visit on Amazon → CRAFTSMAN Storage Organizer 3-Pack |
Three 10-compartment organizers with latched lids | Bulk hardware sorted by class | Shelving above the bench | $28.99 |
Should you buy the Milwaukee Packout?
Yes, if you work in more than one place. It's the best modular system I've used, the cases lock together so the stack stays a stack when you roll it, and the drawers lock tight. The rolling base means you move the whole stack instead of unloading it, which is the entire reason to buy a system instead of four separate boxes.
The catch is that it's a system, so the first purchase is the cheap part. The stack grows, and you'll need somewhere to park it. If you work out of one bench and never leave the garage, save your money and buy organizers instead. If your tools travel, this is the one to build around.
Should you buy the CRAFTSMAN storage organizer 3-pack?
Yes, if your small hardware is currently living in a coffee can. Three organizers with 10 compartments each let you sort by class instead of by pile: one for metric, one for standard, one for electrical. The lid latch is the part that matters, because a latch that pops when you carry the box by the lid dumps your sorted hardware on the driveway and makes you do the job twice.
It's the cheapest way to stop digging for a 10mm, and the 10mm is why you're reading this in the first place.
What about the other two?
The CASOMAN interlocking pair is the upgrade path for anybody who wants adjustable bays instead of fixed ones, and the removable dividers are what make it worth the step up. The Jack Boss is the box for the person who wants one steel carry box with a removable tray and a handle that doesn't saw into their fingers, and 16 inches is the size that stays carryable when it's full.
The bottom line
Buy the storage that matches how your tools move. If they travel, start with the Packout and build a stack. If they don't, spend your money on organizers and a carry box, and put the savings into the tools themselves. A box that organizes five thousand dollars of tools is the best value in the shop, and it doesn't have to be the most expensive thing on the shelf to do it.