Bridge Torque

Definition and importance

Bridge torque refers to the rotational force required to shear the tamper-evident bridges or lugs that connect a screw cap to its locking ring. These bridges are designed to break on first opening, providing a visible indication of tampering and ensuring product integrity.

The ideal bridge torque must be carefully balanced, strong enough to deter tampering, but weak enough to allow consumers to open the package without difficulty. Measuring bridge torque precisely is vital in regulated industries such as pharmaceuticals, medical packaging, and beverages, where both safety and user accessibility are critical.

Too little torque may result in compromised tamper evidence; too much, and the packaging can frustrate or even injure users.

Applications in packaging

Bridge torque testing is especially relevant for tamper-evident and child-resistant packaging. Common applications include:

• PET and HDPE beverage bottles for carbonated drinks, juices, and probiotic beverages
• Pharmaceutical containers with child-resistant features
• Medical sample vials and diagnostic kits

Each of these applications has specific requirements for closure design and torque values, making customised testing essential.

Bridge torque is measured by applying rotational force to a closure until the tamper-evident bridges shear. This is typically followed by continued rotation to measure the force required to fully remove the cap, known as breakaway torque.

Manual torque testers are suitable for R&D environments and lower-volume production, providing digital readouts that depend on consistent operator technique. For higher-volume and regulated production lines, automated torque testing systems offer improved repeatability, data integrity, and traceability. These systems apply precise force, capture torque curves, and automatically flag any deviations from pass criteria.

Types of torque testing in packaging

Several torque measurements are relevant to closure performance:

• Bridge torque – The force required to shear the tamper-evident bridges
• Breakaway torque – The torque needed to start unscrewing the cap after the bridges have broken
• Rundown torque – The torque applied during capping to ensure consistent closure tightness

Accurate measurement of both bridge and breakaway torque ensures packaging provides effective tamper evidence while remaining user-friendly. Inconsistent bridge torque can result in premature failure or unbroken bridges post-opening, both of which undermine user trust.

Manual vs automated testing methods

Manual torque testers

Manual testers are ideal for development labs and low-throughput environments. Compact and cost-effective, they deliver reliable results when used consistently. However, measurements may vary between operators.

Automated torque testing systems

For production environments, automated systems offer software-controlled accuracy and repeatability. Benefits include:

• Controlled, repeatable torque application
• Integration with software for data capture and audit trails
• Programmable pass/fail criteria
• Faster throughput and reduced human error

Choosing the right method depends on production volume, regulatory requirements, and quality control procedures.

The role of bridges in tamper-evidence

Tamper-evident bridges are a critical safety feature. Once broken, they provide a clear visual indicator that a product has been opened. Their design requires careful selection of materials and precise engineering to ensure predictable, consistent fracture under a defined torque.

If bridges are too weak, products may appear tampered with during transit. If too strong, consumers, particularly elderly or disabled users, may struggle to open the container. Reliable torque testing enables packaging engineers to fine-tune closure designs to meet compliance and usability goals.

Ensuring customer safety and satisfaction

In sectors such as pharmaceuticals and nutraceuticals, tamper-evident packaging is not just a quality concern, it is a regulatory requirement. Child-resistant packaging, for instance, must strike a balance between being difficult for children to open while remaining accessible to adults.

Inaccurate torque values can result in non-compliance, recalls, or consumer dissatisfaction. Effective torque testing supports:

• Compliance with safety regulations
• Reduction in product returns and complaints
• Greater consumer confidence and brand trust

Overview of ASTM and CETIE standards

Standardised testing ensures consistency and compliance. Commonly followed guidelines include:

• ASTM D2063 - Specifies methods for measuring the opening torque of child-resistant closures
• CETIE guidelines - Provide technical specifications for testing screw-cap closures on PET bottles, particularly within the beverage industry

These standards define acceptable torque ranges, testing conditions, and documentation practices.

Applying standards in your process

To implement standard-compliant torque testing, manufacturers should:

• Use calibrated, traceable testing equipment
• Maintain consistent testing conditions (e.g. temperature, humidity)
• Record torque curves and results using validated software
• Regularly review torque specifications as part of QA processes

These best practices improve packaging reliability and reduce risks in the market.

Screw-cap torque test on PET bottles

A beverage manufacturer identified inconsistencies in bridge torque linked to capping machine variability. By introducing automated torque testers, they were able to adjust application torque parameters and significantly reduce consumer complaints.

Probiotic drink packaging testing

A health drink producer used manual torque testers to benchmark closure strength across production batches. This enabled them to redesign caps to meet the needs of older consumers while maintaining package integrity.

PET packaging for COVID-19 test kits

During the pandemic, a medical packaging supplier repurposed PET bottling lines for test kit vials. Automated torque testing ensured rapid, compliant validation of tamper-evident features under tight production deadlines.

From manual testers to automated systems

Mecmesin offers a wide range of torque testing solutions suitable for R&D, quality assurance, and full-scale production. Options include:

• VTG Tornado - A portable, manual tester ideal for development and QA labs
• VortexPro System - A programmable, automated tester for production environments

Accuracy, repeatability, and compliance

Mecmesin systems are designed for precision and ease of use. Features include:

• VectorPro software for test control, analysis, and reporting
• Traceable calibration and audit trails
• Configurable pass/fail logic for immediate feedback
• Support for compliance with ISO and GMP standards

These tools help reduce human error and improve packaging performance across batches.

Ongoing support and training

Mecmesin provides global support services, including equipment calibration, user training, and technical assistance. Whether remotely or onsite, our expert team helps ensure your systems remain accurate, compliant, and efficient.

Proven results across industries

Clients in the pharmaceutical, beverage, and medical sectors have reported:

• Reduced defect rates
• Faster validation of packaging changes
• Improved customer satisfaction

Mecmesin torque testing systems deliver measurable return on investment through improved quality and reduced waste.

If your organisation is reviewing its torque testing processes, consider the following actions:

• Assess your current testing methods and equipment
• Evaluate torque specifications for each packaging format
• Explore automation opportunities to improve throughput and consistency

Mecmesin can assist in reviewing existing systems and recommending appropriate solutions.

To identify the right torque testing solution for your packaging, whether in pharmaceuticals, beverages, or medical devices, speak to a Mecmesin specialist. Our team will provide tailored advice and live demonstrations based on your specific requirements.