
The new FLEX Stack Pack tool box system makes good on the brand’s it’s what’s next tagline, delivering features and benefits not shared by any other modular tool box system today.
Flex provided a brief introduction to their new Stack Pack pro tool box system earlier this year, and the new line is ready to launch.
Flex supplied me with a sampling of the new offerings (thank you!), and while I haven’t tested the system thoroughly enough for a full review yet, I’ll mix in firsthand opinions and observations throughout this post.
Note: Flex is a ToolGuyd sponsor.

To start off, Flex Stack Pack is a new modular tool box system. The 3-piece tool box combos are often the most popular way to buy into a new tool box system, but you can create your own a custom kit with whichever individual components work best for your needs and wants.

To start off, there will be a rolling tool box, large tool box, small suitcase-style tool box, organizer, and half-width organizer.
Flex Stack Pack Tool Box Options
- Half-Width Organizer (FS1302)
- Organizer (FS1301)
- Small Suitcase Tool Box (FS1103)
- Medium Tool Box (FS1102)
- Rolling Tool Box (FS1101)
What’s the Big Deal?
Here are the main selling points.

Quick-Connect Latches – The tool boxes have a spring-action auto-connect interlocking mechanism. Place a Stack Pack tool box on top of another, and it auto-locks in place.
From what I have experienced so far, Flex did this exceptionally well, with the tool boxes latching together with minimal fiddling. Disconnecting the tool boxes is easy as well – you press the latches on opposite sides of the lower tool box, and you can then use one or both hands to remove the top tool box.
This is so much easier compared to some other modular tool boxes I’ve used in the past.
Heavy Load Capacity – Flex says their 3pc combo can hold up to 500 pounds of tools, besting comparable and lower priced competitors.
Impact Protection and Metal-Reinforced Corners
IP65 Protection – This matches the water and dust resistance of leading modular tool box systems, and bests the protection level of more value-priced systems.
9″ Rugged Wheels – Larger wheels should help maneuverability across rough terrain. Top competing systems feature 8″ (Dewalt ToughSystem 2.0) and 9″ (Milwaukee Packout) wheels, and others have 7″ wheels (Ridgid Pro, Craftsman TradeStack).

Accessory-Ready – Here’s where things get interesting, with the ability to quickly connect Flex accessory cases within Stack Pack tool boxes.

In addition to inner lid accessory mounting placements, the rolling tool box has two additional positions at the backwall.
Detachable Handle (Rolling Tool Box) – The rolling tool box’s extending handle can be removed for easier storage and transport, such as in a covered pickup truck bed.

Exterior Storage Attachment Racks – Users can mount optional accessory rails to the outside of Flex Stack Pack tool boxes, for even greater customization and mounting options.

Connectable Accessory Cases – Flex’s power tool accessory cases can latch together for easier carrying and storage, independently of the Stack Pack tool box system.
Flex Stack Pack Tool Box Mounting Accessories
- Front Rail Rack (FS1603)
- Side Rail Racks (FS1604-2)
- Adjustable Charger Mounts (FS1606-2)
- Cord Wrapper (FS1605)
- Battery Holder (FS1601)
- Level Holders (FS1602)

An adjustable charger mount allows for Flex 24V cordless power tool battery chargers to be easily mounted inside the large and rolling tool boxes.

There’s also a battery insert, for mounting spare Flex 24V batteries.

The battery holders can also be attached exterior to a Stack Pack tool box, via the optional metal mounting rails.

The available accessories serve two purposes. First, they increase the accessibility of certain tools, avoiding the need to open a tool box or unlatch everything. But, they also increase the amount of gear you can haul in a single trip.
Certain equipment – extension cords, circular saws, spare battery packs, can take up valuable tool box real estate. Not all users will want to put these types of tools or equipment on the outside of a tool box, but with Flex Stack Pack you can if you do want to.
In addition to structural reinforcement, the metal-reinforced corners have threaded mounting holes, which opens a world of customization possibilities.
First Thoughts and Impression
I have purchased into most modern modular tool box systems, and have learned that none of them are perfect.
Flex Stack Pack is certainly different, and it’s better in a lot of ways. Is it the best? Well, that depends on what you’re looking for.
Being able to mount different equipment and accessories – inside and out – is a huge selling point.
So far, I’m quite pleased with Flex’s competitiveness. Stack Pack so far seems to be a well thought out, durable, and convenient tool box system. Its expandability options will be a game-changer for some, especially once 3rd party accessory-makers build upon Flex’s mounting solutions.
If you just need a tool box system to haul your gear around, Flex Stack Pack is one of many fine options.
But if you want a tool box system that can be customized to your liking and preference, this system offers greater flexibility than I’ve seen in competing systems.
Sure, you can drill into, add onto, or modify most brands’ modular tool box systems, but most users don’t want to do this, and are happier for screw-on or snap-in accessories.
I hope to see Flex steadily expand the Stack Pack line in the future, such as with crates, totes, dollies, tool bags, and additional mounting accessories.
Everything has trouble-free so far, from the interlock mechanisms, to the handles and latches.
I think that Flex Stack Pack is going to make some competing brands sweat a little. The new system offers a lot, and with no compromises I could find yet.
Look for it at Lowe’s stores and online at Flex tool dealers.