Security seal manufacturers generally incorporate three (3) main features into their design:
- Tamper resistance: it should not be possible to manipulate the components of the seal without the use of tools. You may see the phrase “tamper-proof” but there are no seals that meet that definition so they must be inspected during transit, if operationally feasible, and at final destination to validate their integrity.
- Resistance to rebuilding: the seal construction should not allow any component part of a used seal to be substituted into another seal of the same or similar design.
- Tamper evidence; the materials used during the seal manufacturing process should ensure that once the seal has been fitted correctly to the truck, trailer, railcar or ocean container, any attempt to open the seal would leave visible evidence.
Manufacturing requirements can vary from company to company but generally the key criteria are pull (tensile) strength, shear cutting strength as well as the ability to maintain structural integrity during bending and impact and in high and low temperature environments. These are part of the requirements set forth in ISO17712, the international standard for Freight Containers- Mechanical Seals. For the more robust barrier seals, drill-resistant hardened metal bodies that contain no soft materials such as zinc are the norm.