How to measure a double seam

Precision is essential when it comes to maintaining the integrity of a double seam. Check that you know what to look for when testing, adjusting, and maintaining your canning machines and ensure can seams are coming in at precisely the right measurement with our handy guide into can double seam measurements. 

Guide to essential can double seam measurements

There are several crucial elements to calculate when seaming to ensure the seam is neither too tight nor too loose. When defects crop up, measurements are the best place to start. Find out more about how to diagnose seam defects using our handy toolkit or familiarize yourself with potential issues with our seam defect glossary.  

Essential seam measurements include:  

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

Seam length/width 

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

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 that becomes the cover hook during the first seaming operation. For a proper curl, you need the following measurements: 

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. Measure using an End Profile Analyzer.  

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 an End Profile Analyzer or manually with a 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 an 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 processes by using an End Profile Analyzer. 

Body hook butting A 

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

Download our can guidebook for information about the process or discover more about the various methods of ensuring the integrity of your process with our full range of double seam inspection options.  

Or, if you’d like a little help figuring out the best testing or inspection solution for your canning line, we’d be happy to help. Our extensive double seam inspection knowledge and beverage testing solutions allow us to offer you the highest quality of packaging, product, and material test and inspection solutions, get in touch to speak with our team.