A bolt seal is a single-use mechanical seal fitted to the locking bar of a container door, consisting of a steel pin and a locking body, that can only be removed by cutting. Its unique number is entered on the bill of lading and customs documents; at destination, an intact seal whose number matches the documents is the primary evidence that the container was not opened en route.
How does a bolt seal work?
A bolt seal consists of two parts: a steel pin with a head at one end and a body containing a locking mechanism. When the pin is passed through the hole of the door locking handle and pushed into the body, it locks irreversibly. The only way to remove the seal is to cut the pin with a special cutter. The body and pin carry the same serial number, the manufacturer's mark and, on most models, a barcode, so that replacing the pin with another body is also detected.
ISO 17712 and class H
The ISO 17712 standard divides mechanical container seals into three classes according to their strength: indicative (I), security (S) and high security (H). Bolt seals used in container shipping are generally sold as class H; check that the class is marked on the seal or in the manufacturer's documentation. The World Customs Organization's SAFE Framework recommends using high-security mechanical seals under ISO 17712 at the point of stuffing. The same text recommends fitting the seal not in the traditional position on the door handle but at a point more resistant to covert tampering. Shipping lines usually issue their own numbered seals.
Who fits it, and where is the number recorded?
- Shipper: Fits the seal as soon as stuffing is complete and enters the number in the shipping documents. For FCL cargo this responsibility lies with the shipper.
- Road haulier: Checks the seal when taking over the container and notes its condition on the document.
- Terminal: The seal and number are checked again at the entry gate.
- Shipping line: The number is entered on the bill of lading and loading lists.
- Official opening: If customs or another official authority cuts the seal for an examination, a new seal is fitted and the new number is entered in the documents.
Difference from a customs seal
| Feature | Line or shipper seal | Customs seal |
|---|---|---|
| Who fits it? | Shipper or carrier | Customs administration |
| Purpose | Evidence of integrity throughout carriage | Assurance that the goods remain under customs control |
| Where recorded | Bill of lading, CMR, declaration | Transit declaration or TIR carnet |
| Who opens it? | The consignee, at delivery | Only a customs officer |
What to watch for when fitting it
- The seal number is read before fitting and recorded in the loading report together with a photo.
- It is checked that the pin is fully seated in the body and does not come out when pulled.
- Unused seals are kept in a locked place; who has taken which number is listed.
- The seal is fitted only after the container door is closed and the locking bars are in place.
- The number written on the document is checked by two people, as even a single wrong digit will cause disputes.
What to do if the seal is broken or the number differs
- Before the container is opened, the seal and door are photographed and the number is compared with the document.
- The situation is noted as a reservation on the delivery document; in road transport the rules for CMR reservations apply.
- The carrier and the insurer are informed immediately; a surveyor is called if necessary.
- For imports, opening and counting take place under customs supervision; missing or excess goods are recorded in a report.
Relationship with electronic seals
An electronic seal adds to the mechanical lock an electronic unit that records or reports the moment of opening. Mechanical integrity is still provided by the pin and body; the electronic part documents the time of the event. Details are in the entry electronic seal.
How does Voltim Global support you?
Voltim Global plans container transport with partner carriers. Vehicles are followed daily; the driver's location is collected via the Voltim mobile app and shown in the customer panel, and the customer receives a daily status report.