Class ‘H’, ‘S’, and ‘I’ Seals: The Differences Explained

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Class ‘H’, ‘S’, and ‘I’ Seals: The Differences Explained

If you are involved in logistics, supply chain management, or loss prevention, you have likely seen the letters “H,” “S,” or “I” stamped on spec sheets or mentioned in compliance regulations. These aren’t just random categories; they are the global standard for keeping cargo safe.

Understanding the ISO 17712 classification is critical. Choose the wrong class, and your cargo could be rejected at customs, easily pilfered, or you might overspend on heavy-duty locks for a lightweight job.

In this guide, we break down the three types of security seals—Indicative, Security, and High Security—so you can choose the exact protection your shipment needs.

Quick Summary: What is the Difference Between H, S, and I Seals?

For those in a hurry, here is the breakdown:

  • Class “I” (Indicative): Designed to show visual evidence of tampering. They are easily broken by hand or light shears. Used for retail totes, airline carts, and meters.

  • Class “S” (Security): Provides a medium level of strength. They require light tools to remove and offer more resistance than indicative seals but aren’t strong enough for international customs.

  • Class “H” (High Security): The strongest barrier seals. They are constructed of metal, require heavy bolt cutters to remove, and are mandatory for C-TPAT and cross-border shipping.

1. Class “I” – Indicative Seals

What they are:
Indicative seals are designed to function as a “witness” rather than a lock. They don’t prevent entry by force; instead, they provide immediate, irreversible visual proof that someone has tampered with the goods.

Key Features:

  • Material: Usually plastic or light gauge metal.

  • Removal: Can be removed by hand or with simple household scissors.

  • Cost: Generally the most affordable option.

When to use them:
Use Class “I” seals when the cargo has low monetary value or when the seal is used on an item that is already physically monitored.

  • Examples: Plastic pull-tight seals on ATM cassettes, duty-free airline trolleys, first-aid kits, and retail distribution totes.

2. Class “S” – Security Seals

What they are:
Class “S” seals occupy the middle ground between indicative vs barrier seals. They offer more durability than a plastic strap but are not strong enough to stop a determined thief with bolt cutters. They create a hurdle that slows down unauthorized access.

Key Features:

  • Material: Usually a combination of heavy plastic and wire, or lighter metal cables.

  • Removal: Requires light tools (wire cutters or pliers).

  • Strength: Medium resistance to pulling and impact.

When to use them:
These are ideal for domestic shipping where C-TPAT compliance isn’t required, but you still want to prevent opportunistic theft.

  • Examples: Domestic truck latches, rail cars carrying bulk commodities, and hazardous waste drums.

3. Class “H” – High Security Seals

What they are:
This is the heavy-duty category. To earn the “H” classification under ISO 17712, a seal must undergo rigorous laboratory testing against impact, shear, bending, and tensile strength. These act as both a seal (showing evidence of tampering) and a high-strength lock.

Key Features:

  • Material: Hardened steel or metal alloys.

  • Removal: Requires large bolt cutters (often 24-inch+) or power tools.

  • Compliance: Mandatory for C-TPAT (Customs-Trade Partnership Against Terrorism) shipments entering the USA.

When to use them:
You generally must use Class “H” seals for any international containerized shipping.

  • Examples: Bolt seals and heavy-duty cable seals (3.5mm diameter or higher) used on shipping containers and cross-border long-haul trucks.

Comparison Table: Choosing the Right Seal

Classification Seal Type Removal Method Primary Goal
Class I Indicative Hand / Scissors Visual Tamper Evidence
Class S Security Wire Cutters Moderate Barrier & Evidence
Class H High Security Bolt Cutters / Power Tools Physical Barrier & C-TPAT Compliance

Frequently Asked Questions (FAQ)

Which seal type is required for C-TPAT?
Only Class “H” (High Security) seals are C-TPAT compliant. If you are shipping goods into the United States, your container must be secured with an ISO 17712 certified High Security seal. 

Can I use a plastic seal on a shipping container?
You can, but it should not be the only seal if the container is moving internationally. Many logistics teams use a plastic indicative seal in addition to a bolt seal for color-coding or additional inventory tracking, but the plastic seal alone does not meet high-security standards.

How do I know if my seal is ISO 17712 certified?
Legitimate manufacturers like Acme Seals will provide certification documents upon request. Additionally, per ISO 17712:2013 regulations, the seal itself must be permanently marked with the letter “H” on the body to verify its High Security status.

Final Thoughts

Selecting the right seal isn’t just about price—it’s about matching the security level to the risk. Using a plastic seal on a high-value electronics shipment leaves you vulnerable, while using a heavy steel bolt on a first-aid kit is unnecessary overkill.

Need help securing your supply chain?
At Acme Seals, we carry a full range of ISO 17712 compliant Class H, S, and I seals. Talk to us to find the perfect fit for your fleet.