Introduction: A serial number turns a one-time cable seal into a readable record at loading, transit, and receiving.
For anyone learning how cargo handovers are documented, the numbered seal is the smallest and most useful piece of evidence in the chain. A plain tag shows that a door was closed; a numbered cable seal also says which trip, which door, and who recorded it. The number is the link between a physical piece of hardware and the loading note, the transit check, and the receiving signature. Following that link from the loading bay to the final check shows why one-time seal designs make a silent swap much harder to pull off.
Every handover record starts with the same small act: someone reads a number off a seal and writes it down. On an indicative cable seal such as the CA-1.5A aluminum cable seal, that number is laser-printed onto the aluminum lock body at the factory, so the characters stay sharp and readable after months of sun, rain, and road dust. The standard 300 mm galvanized cable is threaded through the door hasp and pushed into the lock body, where an internal steel mechanism grips it. The moment that happens, the seal is closed for good, and the loader copies the serial onto the shipment paperwork. That written number is what makes the rest of the trip checkable. Two people can look at the same seal and disagree about whether it matches the one they remember, but a number on a document does not drift with memory or daylight. CTPAT cargo security guidance treats seal numbers as part of the shipment record, and the World Customs Organization's transit guidance follows the same logic: the seal identifies the load, and the document identifies the seal. A workable handover entry usually carries four things — the seal number, the date and time it was applied, the location, and the person who closed it. Laser-printed serials are intended to serve as unique identifiers, which is exactly why they are worth copying carefully instead of casually. The comparison itself is manual: a person reads a number on a lock body and matches it against a line on a document. That step is what turns a printed serial into a usable record, and it is also what catches a mismatch early. The same discipline holds whether the seals arrive from a large aluminum cable seal manufacturer or a regional cable seal supplier — the number only works if one person records it and another person reads it back.
A numbered seal does not need to be heavy for the number to matter, but the physical design is what closes off the easiest tricks. Inside the lock body, a steel mechanism grips the cable in one direction only. Once the cable is pushed in, pulling it back out is not possible; the only way to open a sealed door is to cut the cable. The tamper-evident behavior here is mechanical rather than electronic. The CA-1.5A uses galvanized wire that is non-preformed, meaning the strands are not shaped to hold a twist. Cut that wire and the strands spring apart, leaving a frayed end that cannot be threaded neatly back into a lock body. A tidy re-seal using the original cable is not realistic. Swapping in a different seal runs into a different problem: the number changes. An indicative cable seal certified to ISO/PAS 17712 "I" class is built for exactly this reading role — it shows interference rather than resisting heavy force, which is why the marking on the outside carries most of the security value. A 330 kg breaking strength on a 1.5 mm cable also means the wire will not snap from ordinary handling, stacking, or road vibration. If the cable turns up broken, the cause is a deliberate cut rather than wear. That distinction matters to whoever has to decide whether to accept a load at the gate. A serial number points to what was sealed, when, and by whom; sorting out who tampered with a load afterward depends on the whole handover file, not on the number on its own. What the number does is remove the easiest excuse. A door resealed with a fresh seal cannot pass as the original, because the new seal carries a new number while the paperwork still shows the old one. The mismatch is visible to anyone holding the record, and it turns a quiet swap into a question that has to be answered on the spot.
Numbered cable seals are not read once; they are read every time the load changes hands. The sequence below shows what each reading is actually for.
Not every trip needs the same number of entries. A short run with one driver and one receiver may only produce two record points, while a multi-leg route can pass through three or four. The rule that holds is simple: write the number down wherever responsibility moves to another person or company, because that entry is the only link between the seal and the custodian who accepted it.
A serial number is a small piece of printed text, but it is what makes a cable seal readable across a whole journey. The seal is closed once at loading, the number is written down, and every later custodian compares what they see against what the record says. One-time locking and non-preformed wire make that comparison meaningful, because the original seal cannot be put back the way it was. Anyone who wants to see how a laser-printed serial appears on an indicative seal, along with the 1000-piece box packing, can review the CA-1.5A aluminum cable seal specifications.
A：It gives everyone the same reference point. The number applied at loading is written on the shipping document, so each later custodian can compare the number on the seal with the number on the paperwork and confirm the load is the one that was sealed at the origin. Without a number, that check turns into a vague conversation about how the seal looks.
A：The replacement carries a different number, so the mismatch shows up at the next comparison. A cut non-preformed cable also frays and cannot be rethreaded, so a resealed door usually shows two signs at once: a different number and a disturbed cable end. Both get noted in the handover record.
A：Recording at every point where custody changes is the strongest habit, since each entry ties the seal to the person who accepted it. On a short run with one driver and one receiver, two entries may be enough. The practical rule is to record wherever responsibility moves to another person or company.
SP 800-88 Rev. 1, Guidelines for Media Sanitization
Customs Trade Partnership Against Terrorism (CTPAT)
