Seamers are machines that bind the ends/lids to the cans using a double (or in some cases, a triple) seam. There are many seamers for different type of material (Steel and Aluminum are the most common) of various material thickness depending on the type of can.
A seamer is composed of one or more seamer heads. Each seamer head should be considered a different (separate) machine, in terms of statistics (6-sigma) and reports. There are single headed seamers and up to 24 headed seamers. 4, 6 and 12 headed seamers are the most popular – with the number of seamer heads increasing as the speed of the line needs to be faster.
There are many types of seamers and seamer manufacturers varying in specialty – some specializing in food cans, some in aerosol, some in high-speed beverage and some focusing on craft brewing (typically lower speed without as many heads).