How to measure a double seam

The trusty double seam is relied upon by can makers and can fillers across multiple sectors as it protects all types of products with a robust, hermetic seal. 

An effective double seam is crucial to the integrity of a can. It creates a seal between the can body and lid (also known as the can end) by mechanically interlocking five layers of metal together.  

Browse through our seam inspection solutions here.

Whether you work with food, beverages, pharmaceuticals, or inks and coatings, a well-constructed double seaming operation is essential to your canning line to protect against leaks and contamination.  

Maintaining the integrity of a can seam can be tricky. You’ll need to measure the seam precisely to ensure it matches specifications and offers the right levels of protection. 

There are several key parameters to calculate when seaming to ensure the double seam is neither too tight nor too loose. When defects crop up, measurements are the best place to start.  

Essential double seam measurements

Cover/end hook length

The cover hook, also known as the end hook, is the measurement of the curled end of the lid during the formation of a double seam.   

The body hook length

The dimension of the can’s flange will change once the double seam has been fully completed. This can be measured in a non-destructive way, using a seam inspection system.  

Seam thickness

The seam thickness is the total width of the entire double seam once curled and completed.   

Seam length/width

This is a critical external measurement of the dimension – top to  bottom – of the double seam (parallel to the hooks of the seam). It can be measured manually with a seam micrometer or automatically with seam inspection software such as the CMC-KUHNKE QbyV SEAMetal SPC.   

Overlap

The width of the outer side of the double seam as it interlocks over the body wall.  

Countersink

The total height of the entire double seam once curled and completed.   

Body wall thickness

The width of the can’s body.  

Average can seam specifications

Other essential measurement components for the double seam process include:  

Lid/end/cover curl

The round edge of the can lid, or end, becomes the cover hook during the first seaming operation.  

Curl radius

On a finished and unseamed can end, the curl radius is the end of the cut edge to the start of the seaming panel.  

Curl height

On a finished and unseamed can end, the curl height is the height from the cut edge to the start of the seaming panel. Measure automatically with the CMC-KUHNKE QbyV End Profile Analyzer, or manually with a CMC-KUHNKE Seam Height Gauge.   

Curl width

On an uncurled can end, the curl width is the distance from the straightened edge to the chuck fit. This measurement – and the uncurling process –isn’t necessary if using the End Profile Analyzer, which can measure curl width even on finished ends.  

Uncurl length

The measurement of the cut and straightened end curl. As with the curl width, this can be measured without the uncurling process by using the End Profile Analyzer.  

Body hook butting A

Body Hook Butting (or BH Butting) is a calculated percentage determining how much of the Actual Body Hook is embedded into the seaming compound.  

Body hook butting B

Body Hook Butting (or BH Butting) is a calculated percentage determining how much space there is available for the Body Hook in the seam.   

You can find out more about how to diagnose seam defects using our handy toolkit or familiarize yourself with potential issues with our seam defect glossary.   

Typical double seam defects

Can manufacturers and fillers encounter a number of common double seam defects, all of which our devices can solve. From buckling and creasing  to false seams and spinners, you can read some double seam terminology and learn about common problems through our glossary of seam defects blog.  

Industrial Physics double seam inspection equipment

Across the Industrial Physics portfolio, we make a wide range of double seam inspection tools and accessories.  

Our SEAMetal double seam inspection devices combine highly accurate optical technology with easy-to-learn, intelligent software. Our SEAMetal systems offer the most flexible solution for double seam testing available in today’s marketplace.  

The SEAMetal range includes everything from handheld devices like the SEAMetal Portable through to the SEAMetal HD: double seam inspection for food cans and our SEAMetal machines developed for craft breweries. 

Across the full catalog of double seam inspection options, you’ll also find SEAM Doctor powered devices like the SEAMetal HD for aerosol cans. 

Masters of metal packaging

At Industrial Physics, we have the finest seam inspection engineers on the planet, and we like to share our expertise. As well as the informative Industrial Physics Seam School platform, we publish blogs like this one – a glossary of double seam defects and this article on how to measure a double seam. 

Whatever the double seam defect you need help fixing , we’re bursting at the seams to support you! 

Contact us – Industrial Physics