# Shipping Container Locks & Seals

Source: https://contsize.com/shipping-container-locks/ · CC BY 4.0 · checked 2026-10-29

The standard way to lock a shipping container is a lockbox — a steel shroud welded or bolted over the hasp on the right-hand door — with a hardened padlock or a puck lock inside it: the shroud keeps bolt cutters and grinders off the shackle. Alternatives and additions: crossbar locks that clamp both lock rods, hidden-shackle puck locks, and GPS smart locks for fleets. Shipping is sealed rather than locked: US law requires an ISO 17712 seal on every loaded container arriving by sea that can take one, and CTPAT asks its members for a high-security class “H” bolt or cable seal fixed right after stuffing — a seal is evidence, a lock is a barrier, and a secure container in transit carries both.

Container security is asymmetric: the box is 1.6–2.0 mm of Corten steel that laughs at crowbars, while the factory door hardware — four lock rods, cam keepers and two handle hasps — was designed to keep doors shut at sea, not to resist a cheap bolt cutter on a cheap padlock. Every real-world container theft targets the same three points: the padlock shackle, the hasp rivets, and the door hinge pins. Every effective lock system defends exactly those points.

This guide covers the hardware in the order the market uses it: the lockbox that should be on every static container, the lock types that go in or on it, and the tamper-evident seals — a different tool for a different job — that secure containers in transit. Door hardware anatomy is in the [door dimensions guide](https://contsize.com/container-door-dimensions/).

![Rear end of a shipping container, not to scale: four lock rods with cam keepers, handles and hasps, hinges.](https://contsize.com/figures/container-door-locking-hardware-en.png)

*Container door hardware: lock rods, hasps, lockbox and seal*

![End view of a 20 ft container whose door opening is 2,340 mm wide and 2,280 mm high.](https://contsize.com/figures/container-door-opening-dimensions-en.png)

**The numbers in this chart**

*What fits through the door opening*

| Item | Width, mm | Height, mm |
| --- | --- | --- |
| Opening | 2,340 | 2,280 |
| Container end, external | 2,438 | 2,591 |
| EUR pallet + pallet truck | 1,200 | 1,700 |
| Passenger car | 1,850 | 1,500 |
| Racking bay 2.2 m | 1,000 | 2,200 |

*What fits through the door opening Drawn to scale; the three sizes are examples*

## The lockbox: a steel shroud over the shackle

A **lockbox** is a steel shroud — folded from heavy plate, with no standard size — welded to the right-hand door leaf, with a matching staple plate on the left leaf that its slot drops over. The padlock hangs *inside* the box, reachable only through a hand-slot from below.

The lockbox’s geometry is the security, three ways over:

- bolt cutters cannot reach the shackle at a working angle;
- an angle grinder must cut the shroud plate first: minutes of sparks and noise, versus seconds on an exposed shackle;
- hammer attacks hit plate, not lock.

Many used containers already carry one — worth checking when [buying](https://contsize.com/buying-a-shipping-container/). Bolt-on retrofit versions exist for owners without a welder; through-bolted with the nuts inside, they give up little. Insurers often ask for a lockbox on jobsite containers, and it is the best-value security spend on this page.

## Lock types compared: what each resists and where it gives way

*Container lock options*

| Type | Fits where | Resists | Weak point |
| --- | --- | --- | --- |
| Hardened padlock | Lockbox or hasp | Cutting, drilling (boron shackle) | Exposed shackle if no lockbox |
| Puck lock (hidden shackle) | Lockbox or welded hasp | Bolt cutters entirely — no reachable shackle | Quality of the mounting hasp |
| Crossbar / bolt-on bar lock | Clamps both door lock rods | Prying, single-door attacks | Visible; quality varies widely |
| Heavy chain + padlock | Around both handle hasps | Casual attack only | Any bolt cutter |
| GPS smart lock | Hasp or lockbox | Adds alerts, tracking, audit log | Battery and subscription; physical rating varies |

Selection logic: for a static storage box, **lockbox + hardened padlock** (or a puck lock, which removes the shackle problem entirely) is the standard answer. A crossbar adds a second, different attack problem for high-risk sites. Chains are a stopgap.

GPS smart locks earn their subscription on fleets and remote sites, where the alert matters more than the steel. Pair one with [container tracking](https://contsize.com/container-tracking/) practice, not instead of a mechanical lock.

The shackle spec if buying a padlock:

- boron or hardened steel;
- the thickest shackle that still passes the lockbox staple;
- a closed-shackle pattern.

Lockboxes are not standardised, so measure the lockbox’s hand-slot before choosing the padlock’s body.

## ISO 17712 bolt and cable seals: evidence, not a barrier

A **seal is not a lock** — it is evidence. It proves one thing: the doors have not been opened since sealing. Two kinds of seal do that job:

- a **bolt seal**: a steel pin snapped into a one-way barrel through the door hasp, cut off with bolt cutters at destination;
- a **cable seal**: a wire rope cinched through both lock rods.

Each seal carries a unique serial number recorded on the [bill of lading](https://contsize.com/glossary/bill-of-lading/). A broken or mismatched seal at destination triggers a cargo claim and an insurance trail.

**ISO 17712** grades seals in three classes by tested strength:

- **“I” (indicative)**: plastic ties that only show tampering;
- **“S” (security)**;
- **“H” (high security)**: bolt and cable seals that hold at least 10 kN in tension and 3.336 kN in shear, survive 501 bending cycles and take 40.68 J impacts, as an accredited laboratory’s test report quotes ISO 17712:2013.

US law (6 U.S.C. 944, CBP Dec. 08-30) requires an ISO 17712 seal, marked with a unique number, on every loaded container arriving by sea that can take one (tanks and open tops are exempt).

The **CTPAT** minimum security criteria require a class H bolt or cable seal on every sealable shipment of a CTPAT member. The shipper or packer fixes it right after stuffing, with the seal’s laboratory certificate on file.

A seal’s cost is trivial against the cargo. In practice:

- put the seal where CTPAT’s guidance does: on the secure cam position at the bottom of the centre-most vertical bar of the right door;
- where the door has no secure cam, put the seal on the centre-most left-hand locking handle of the right door;
- photograph it with its number;
- verify the number (not just presence) at destination;
- treat any discrepancy as a claim event.

## Theft-proofing checklist: six steps by value per dollar

The theft-proofing steps, in descending order of value per dollar:

1. **Fit a lockbox** — the shroud defeats the tool every casual thief carries.
2. **Put a real lock in it** — a boron-shackle padlock or a puck lock; a cheap padlock wastes the lockbox.
3. **Doors toward light and sight** — face a wall so doors cannot swing (dead storage), or face the house/camera/road (active use); thieves work unobserved ends of yards.
4. **Defend the hinges** — hinge pins are the forgotten flank; weld a tab over accessible pins or choose containers with interior-welded pins.
5. **Light and camera** — a solar motion light on a container in view beats extra steel on one behind a hedge.
6. **Photograph contents and the container number** — recovery and insurance both start from the [unit’s ISO number](https://contsize.com/conex-box/).

For jobsites, add one more: empty the box of power tools before long weekends, which is when containers are opened.

## Where locks fail: the five weak points

Post-incident patterns repeat. Container locks fail at five points:

- **The exposed shackle**: any padlock hung bare on the handle hasps dies to a long-handled bolt cutter in seconds. Without a lockbox, lock quality barely matters.
- **The hasp, not the lock**: factory handle hasps are riveted; thieves drill or shear the rivets and lift the whole assembly, lock intact. Welded hasps or a lockbox close this gap.
- **The hinges**: grind two pins, and the door opens backwards on the locked side.
- **The second door**: the left leaf’s lock rods hold it shut; a crossbar or interior slide-bolt on the passive leaf stops pry attacks that peel it.
- **The forgotten grinder**: nothing on this page survives an unhurried battery grinder. The lockbox plate buys minutes and noise, not immunity.

Time, noise and visibility are the actual security products. Every layer of container security buys more of all three.

## Frequently asked questions

**What is the best lock for a shipping container?**

A lockbox (a steel shroud welded over the right-hand door’s hasp) with a boron-shackle padlock or a hidden-shackle puck lock inside it. The shroud defeats bolt cutters, the hidden shackle removes the standard attack entirely. Add a crossbar lock on high-risk sites.

**How do you lock up a shipping container?**

Static storage: padlock or puck lock inside a lockbox on the right door, optionally a crossbar across both lock rods and a slide bolt on the passive leaf. In transit: an ISO 17712 class H bolt seal through the hasp, serial recorded on the shipping documents — plus a padlock where the carrier allows.

**What size padlock fits a container lockbox?**

One whose body passes the lockbox’s hand-slot and whose shackle reaches through the staple inside — lockboxes have no standard size, so measure the slot, or take the lock the box’s maker names, before buying. Choose closed-shackle or shrouded patterns and boron-alloy shackles — inside a lockbox, drill resistance matters more than cutter resistance.

**What is the difference between a container seal and a lock?**

A lock is a barrier — it resists opening. A seal is evidence — a serial-numbered bolt or cable that must be destroyed to open the doors, proving en route that no one did. Shipping lines and customs work with seals (ISO 17712), site security works with locks, and a laden container in transit properly carries both.

**What is an ISO 17712 high-security seal?**

A bolt or cable seal that passed ISO 17712’s class “H” tests — at least 10 kN in tension and 3.336 kN in shear, 501 bending cycles and 40.68 J impacts, as a laboratory’s test report quotes the 2013 edition — and carries a unique number. CTPAT’s criteria require one on every sealable shipment of a CTPAT member, fixed by the shipper or packer right after stuffing.

**Can thieves break into a locked shipping container?**

Given time, tools and privacy — yes; a battery angle grinder defeats any hardware eventually. Practical security stacks delay and exposure: lockbox plus quality lock (minutes of loud grinding instead of seconds of silent cutting), protected hinge pins, lighting, sight lines and cameras. Most attempts stop at the lockbox.

**Are shipping containers secure for storage?**

More than any shed or trailer: 1.6 mm corrugated Corten walls, 2.0 mm steel roof, 2.0 mm steel doors (as builders’ specifications print them) and no windows leave the doors as the only practical entry. Fit a lockbox and a hardened lock and the box outclasses everything short of a vault — the weak points are always hardware, never the shell.

**Do container doors lock without a padlock?**

No — the factory handles and cam keepers hold the doors closed and weathertight, but anyone can rotate them. Security is entirely the added hardware: padlock, puck lock, crossbar or seal through the hasps. An unlocked container is open; assume nothing about the handle mechanism.

## Related pages

- [Container door dimensions2.340 m wide · 2.280 m high · smaller than inside](https://contsize.com/container-door-dimensions/)
- [Container trackingCheck the digit → name the owner → open the tracker](https://contsize.com/container-tracking/)
- [Buying a container: checklistInspect · Grade · Price · Deliver](https://contsize.com/buying-a-shipping-container/)
- [Container grades & conditionOne-trip → IICL → CW → WWT → as-is](https://contsize.com/container-grades/)
- [Storage container sizes8 · 10 · 16 · 20 · 40 · 45 · 48 · 53 ft](https://contsize.com/storage-container-sizes/)
- [Conex box & container namesCONEX = Container Express · since 1952](https://contsize.com/conex-box/)