Buying a Used Cargo Box: What to Check
November 8, 2026 · 11 min read
A used Thule cargo box at a third of the new price looks like an easy win, until it is in your driveway with no keys, no clamps and a lid that drops on your head. Those three parts separate a bargain from a 50-pound plastic shell. Here is what to check, in the order that matters.
Updated — first published
Quick answer
Check three things on a used Thule cargo box before you pay: that all four mounting clamps are in the box, that a key turns in both locks, and that the lid stays up on its own. A box missing its hardware or its keys can cost more to put right than the box is worth.
The short answer
Buy the complete box, not the clean one. A scratched box with four clamps, two working locks and a lid that holds itself open will serve you another decade. A spotless box with none of those is a parts order.
This is for you if
- You are going to look at a box in someone’s driveway
- You already have crossbars and want to spend on the box, not the rack
- You use a box two or three times a year
Look elsewhere if
- Your car has no crossbars and no factory rails, where a hitch tray costs less than a rack plus a box — see our best hitch cargo carriers (2026)
- You park in a low garage and plan to leave the box on the car
Check this before you drive over
Measure your crossbar spread first. A crossbar is the bar running across your roof, and most boxes need their mounting points 24 to 36 inches apart. If your bars sit closer than the clamps can reach, the box does not fit your car at any price.
Your crossbar type and spread
Note whether your bars are round, square, aero or a factory bar with a T-track slot, then ask whether the box’s clamps open around an aero bar.
Your roof load limit, not the box’s
Three numbers apply: the box’s load rating, the rack’s dynamic load rating, and your car’s roof load limit. The lowest is your real limit, and the empty box, 30 to 55 pounds, comes out of it first.
Which side it opens, and what you carry
Dual-side opening is worth paying for if you load alone or park on the street. For skis, inside length beats volume: our best ski and snowboard cargo boxes (2026) guide covers those shapes.
The number that barely matters: cubic feet
Two boxes of the same cubic feet hold different things, one long and shallow, the other short and tall. Ask for inside length, width and height instead.
Checking the lid and hinges
Open the lid, let go, and count to ten. A lid that stays up has working lid lifters, the gas struts or sprung hinges that hold it; a lid that sinks needs them replaced, and they sell per side.
Then press the rubber seal strip where lid meets base. It should spring back. Flattened or cracked seal means water in your duffel bags on the first wet highway mile.
Last, look at the plastic from inside with the lid open. Hairline cracks running from a mounting hole or hinge mount are the only damage that should scare you, because that is where the load goes. Scratches and chalky fading are worth a discount, nothing more.
Lock cylinders and missing keys
Ask for the keys before you ask the price, and turn one in every lock. Thule’s One-Key System stamps a code on the key shank, the letter N and three digits such as N217; Yakima’s Same Key System stamps the letter A and three digits on each lock core. A dealer matches a key to either code, and Thule’s keys and locks page is where to start.
The trap is a box locked shut with no key. On both systems the core must be unlocked before a control key can pull it out and show its number, so a locked box with no key means drilling the core out. That is a job, not a check.
Mounting hardware: the expensive piece
Mounting hardware is the thing most often missing and the most expensive to replace. It is the four clamps, cradles or U-bolts that sit in the floor of the box and grip your crossbars, and every generation uses a different set.
Count four assemblies, then work one to check the thread or ratchet still turns. Thule’s current boxes use PowerClick clamps that click when tight; earlier ones used Quick Grip cradles, Quick Snap fittings, EasySnap housings or plain U-bolts with backing plates. They do not interchange: the T-track adapter kit that bolts a box into a 20 mm T-track slot fits PowerClick boxes only.
The brand-by-brand inspection checklist
Which part goes missing depends on the brand and generation. The last column decides the price you offer.
| Brand and generation | Part most often missing | How to check it | If it is gone |
|---|---|---|---|
| Thule, PowerClick era Motion XT, Force XT, Motion 3, Force 3 | PowerClick mounting clamps, four per box | Count four clamp assemblies in the floor; turn a knob until it clicks | Clamps sell one at a time, so four is the biggest line in the repair |
| Thule, Quick Grip era Ascent 1700, Atlantis | Quick Grip mount assemblies and their cradles | Look for four cradles seated in the floor channels, not loose in a bag | Still sold singly for Ascent, Atlantis and Force, but not for the Evolution |
| Thule Evolution, Cascade | The original mounting hardware set | Four U-bolts with backing plates and wing nuts, plus the plastic slide strips | The original hardware is discontinued; an EasySnap or U-bolt kit is the usual substitute |
| Yakima SkyBox, Space Case | The key, and sometimes the whole SKS lock core | Read the code on the core, the letter A and three digits, and work both latches | A core pulls out only while unlocked, so a locked box with no key means drilling |
| SportRack and Sears X-Cargo | Lock cores and the small hardware bag | Check both lock faces for a stamped number and shake the box for loose fasteners | Many take Thule-type N-series cores, so locks are fixable; odd fasteners are not |
What a driveway check cannot show you
Stress cracks hide under the clamps and floor mats, and nothing shows until the box is off the car. If the seller will let you lift it onto the lawn, photograph each mounting point.
Discontinued models and parts
An older model is fine as long as its parts are still listed, and that takes two minutes to check before you leave the house. Search the model name on Thule’s spare parts and instructions page, or on Yakima’s product info lookup with the discontinued-products box ticked, which also gives the years a model was made.
Look for whether the mounting hardware and lid lifters are still listed, not whether the box is still sold. Plenty of discontinued boxes still have keys, hinges and slide strips; a few have nothing but keys. The Thule Evolution is the one to know: its mounting hardware was discontinued while replacement keys stayed easy to get. If a model lists no parts at all, buy it only if it is complete.
What a fair used price looks like
Start from what the same box costs new today, then subtract every missing part before you talk about age or scratches. A complete box and an incomplete one are different products, and sellers price them the same.
Replacement tiers give you the numbers. A pair of lock cores with keys sits in the under-$50 tier, and a lid lifter is usually a sub-$75 part per side. Mounting hardware bites hardest: a snap-mount or T-track set lands in the $60 to $150 tier, and clamps bought one at a time climb past it. Against a new box from our best roof cargo boxes (2026) guide, a hardware-free box at half of new is no deal.
Pay up for a complete, keyed, current-generation box. Treat one missing hardware as a shell worth parts money.
Key terms, explained
Three words come up in every listing and parts catalog, and getting them wrong is how people buy a box that will not mount.
Plain-language definitions
- Lock core (also called a lock cylinder)
- The removable barrel your key turns, stamped with its own code: N plus three digits on a Thule, A plus three digits on a Yakima. You order a replacement key by that code.
- Lid lifter
- The gas strut or sprung hinge that holds the lid open while you load. It is a wear part, sold per side, and a lid that will not stay up has a failed one.
- Dynamic load limit
- What a roof rack is rated to carry while the car is moving, which is lower than parked. It covers the box plus its contents, so an empty 50-pound box has used part of the allowance.
When to walk away
Walk away from a locked box with no key, every time. It is the one fault that turns a cheap box into a drilling job before you use it once.
- It is locked and the keys are long goneNeither Thule nor Yakima cores pull out while locked, so the core has to be drilled and replaced first.
- No mounting hardware and a discontinued modelClamps you cannot buy means improvising, and improvised hardware on a roof at 70 mph is not worth the saving.
- Cracks at the mounting points or hinge mountsThat is the loaded part of the shell, cracks there spread, and nobody sells a replacement base.
- It does not clear your tailgate or garageMeasure your crossbar spread and garage height before you go, not after it is on the roof.
How this guide was researched
Cedar Buy built this checklist from manufacturer parts catalogs and support pages, not from listings, so the parts named here are ones you can still order.
How this was put together
- Thule spare-part and keys-and-locks documentation and Yakima’s product info lookup, discontinued models included, were read in November 2026.
- Mounting systems were weighted most heavily: hardware is the most often missing part and the least interchangeable.
- Cosmetic condition was left out on purpose, being the easiest thing to judge from a photo.
- Price bands here describe segments of the replacement-parts market, not current listings, and prices change.
- Specifications come from manufacturer documentation. Cedar Buy does not physically test products — see our editorial policy.
Frequently asked questions
Can you get replacement keys for a used cargo box?
Yes, as long as you have the code. A Thule key carries the letter N and three digits on its shank, Yakima stamps the letter A and three digits on each lock core, and a dealer matches a key to either. With no key and no visible code, the core has to come out first, and that needs a control key and an unlocked core.
Will a used Thule cargo box fit my crossbars?
It fits if the box’s mounting system suits your bar shape and your spread falls in the box’s range, usually 24 to 36 inches. Aero bars are the usual problem, because older clamps and U-bolts often will not open far enough around a wide bar. Measure center to center before you go.
Is a used cargo box with no mounting hardware worth buying?
Only if you price the hardware first and the seller takes it off. Four clamps or a snap-mount kit can cost as much as a cheap used box, and some discontinued boxes have no hardware at all. Look the model up on the maker’s spare-parts page while you are still in the driveway.
What to do next
Before you drive anywhere, ask the seller for three photos: the inside floor with the mounting hardware, both locks with the keys in them, and the lid propped open on its own. Those three answer the questions that decide the price.
If they all come back good, go and look, then negotiate on scratches. If one comes back missing, price that part first and offer parts money.
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