Strip Torque

Definition and importance

Strip torque testing measures the torque required to continue rotating a threaded closure beyond its normal sealing point until the thread strips or the closure fails. It reveals the strength of the thread engagement, the quality of materials, and the performance of tamper-evident features.

The primary objectives are to:

• Prevent over-tightening which can damage closures, compromise seals, or make opening difficult
• Verify that closures meet safety and regulatory standards
• Detect manufacturing inconsistencies that could cause product failure

For packaging, correct strip torque values ensure the closure maintains its seal without risking damage during capping. In medical devices, the method confirms that connectors such as Luer fittings meet safety requirements without risking leakage or accidental disconnection.

Common applications

Packaging industry

In food, beverage, pharmaceutical, and cosmetics sectors, strip torque testing verifies that closure systems such as plastic screw caps, aluminium lids, or metal closures are applied within the correct torque range. This ensures packaging remains sealed throughout its shelf life, consumers can open the product without excessive effort, and tamper evidence is preserved. Typical applications include PET bottle caps, glass jar lids, and aseptic packaging closures. For example, strip torque for PET bottles is often within 1 to 3 N·m depending on size and application.

Medical devices and healthcare

In healthcare, precision in torque measurement is critical. Luer connectors used in syringes and infusion systems must meet ISO 80369-20 requirements for secure, leak-free connections. Medical packaging, such as vials and blister packs, may also require torque verification to maintain sterility. Torque values in medical applications are often measured in mN·m, with very low tolerances to ensure safety without damaging components.

ASTM standards

• ASTM D3470 - Procedures for measuring closure torque and assessing performance under applied stress
• ASTM D3474 - Guidelines for calibrating torque measuring devices to ensure accuracy and repeatability

CETIE guides

CETIE (International Technical Centre for Bottling) issues industry guidelines, for example:

• Guide 2 - Torque application for plastic caps on PET bottles
• Guide 5 - Torque specifications for aluminium roll-on closures
• Guide 9 - Torque for closures on glass bottles

These guides are widely used to ensure closure systems function correctly under real-world conditions.

ISO standards for child-resistant packaging

BS EN ISO 13127 - Mechanical test methods for child-resistant packaging, including strip torque testing to confirm safety while maintaining accessibility for intended users.

Equipment used

Strip torque testing can be carried out using:

• Manual torque testers for quick in-process checks
• Digital torque meters for higher accuracy and peak torque capture
• Automated torque testers such as the Mecmesin Vortex and HelixaPro for repeatable tests with programmable control

Mecmesin’s range includes the HelixaPro for low torque precision, the Orbis Digital Torque Tester for portable accuracy, and the Vortex range for automated testing. Other systems, such as the MultiTest-dV and OmniTest, can be configured with torque sensors for combined force and torque testing. All equipment is compatible with Mecmesin’s VectorPro software for data capture, analysis, and reporting.

Calibration and accuracy

Accurate measurement depends on correct calibration. ASTM D3474 outlines standard procedures for torque device calibration. Regular calibration ensures consistency, reduces the risk of faulty product release, and maintains compliance with customer and regulatory requirements.

Luer connector testing

A medical device manufacturer needed to verify strip torque for Luer connectors used in IV systems. Using the HelixaPro with a precision torque cell, the test was performed to ISO 80369-20. The results enabled the manufacturer to optimise the production process, improving patient safety and reducing leakage risk.

Multi-way plastic beverage closures

A beverage producer required testing for multi-way closures on carbonated drink bottles. Mecmesin developed a custom fixture to hold and rotate the closure while recording strip torque. This confirmed that closures retained gas over extended storage while remaining easy to open.

Mecmesin offers a complete range of high-precision torque testing instruments designed for packaging, medical, and industrial applications. Our systems meet ASTM, ISO, and CETIE requirements, deliver high repeatability and accuracy, and can be adapted to closures of different sizes and materials.

With decades of experience supporting manufacturers worldwide, we can help you select the right strip torque testing solution for your application, from portable digital testers to fully automated systems integrated with VectorPro software. Speak to an expert about strip torque testing today.