Different materials can be used to manufacture a metal seal.
b. Aluminium foils
c. Aluminium small blocks
Lead has been used to manufacture seals starting 3.000 years ago, and up to now is still used either for security seal for customs or for decorative seal.
It can be applied only by means of special pliers, which engrave a mark onto the metal.Starting half of the last century aluminium foils are also used, conveniently cut in small stripes having variable width (from 7 to 10 mm). Alongside the strap a progressive numbering can be carved by a printing press.
This kind of metal seals are very easy to use and have a very inexpensive price.
They are also called “indicative seals”.
A very interesting realisation of metal seal dates back to 1970, when seals with aluminium body are realised, out of which a steel cable in variable length springs.
This kind of metal seals are adjustable and offer a high resistance to traction, so that they will be classified later on as high security seals.
The aluminium body, available in different colours, can be customised with numbering and printings.
With the increasing need for metal seals featuring higher and higher robustness and security, in the same period full metal bolt seals were designed and manufactured, which will have been using more or less exclusively to seal containers.
The strongest and most secure seal currently available on the market is a bar seal, used to block the central locking bars of containers.
Both bolt-lock seals and bar seals qualify as high security seals, as well as cable seals – having cable diameter higher than 3.5 mm – do.
All of these metal seals can qualify as high security seals when compliant with the technical requirements expressed within the international standard ISO 17712: 2013, which applies for mechanical seals used for freight containers.
Some countries, like USA for example, accept incoming international cargos and containers only when sealed with ISO 17712: 2013 compliant seals.