let me tell you what is Metal seals

Metal seals

An ISO17712 compliant bolt security seal on a shipping container 

High security bolt seal attached to a shipping container.
There are several basic designs of the metal seals; bolt seals, ball seals and cable seals.

Bolt seals are used to secure shipping containers, trucks and trailers. A bolt seal used for securing containers must conform to the ISO 17712 high security seal in order to be accepted by customs all around the world in ocean shipping. The C-TPAT (Customs Trade Partnership Against Terrorism) specifies ISO 17712 compliant security seals to be used. Bolt seals are generally closed by hand (by pushing the seal body and head together) and opened with the use of bolt cutters. This gives a strong and secure seal for transportation, while remaining convenient for staff in ports and warehouses. All ISO 17712 compliant seals are numbered on both seal body and head, to prevent substitution of either part. This is usually done using laser marking, which cannot be rubbed off.

Ball seals are commonly used for securing trucks. They consist of a metal strip with a punched hole, attached to a housing section. When the strip is bent and threaded through the hole, a ball inside the housing section locks it in place. Most ball type seals belong only to the indicative level as to ISO 17712.

Cable seals allow for more versatile application, as they have variable length of the locking mechanism limited only by the cable length. Typical applications include sealing trucks and railway cars transporting valuable commodities. An internal locking mechanism prevents the cable from being retracted. Most cable seals are classified as security or high security level as to ISO 17712.