http://www.empac.eu/index.php/site/section/198
http://www.empac.eu/uploads/files/115/3f3f518639bb67aff968c3...
Three-piece cans, which were developed in the middle of the 19th century, consist of a cylindrical body rolled from a piece of flat metal with a longitudinal seam (usually formed by welding) together with two can ends, seamed on to each end of the body. Three-piece cans, made from steel, may be made in almost any practical combination of height and diameter. This process is particularly suitable for making cans of mixed specifications as it is relatively simple to change the specification of can being made.

Two-piece cans are made from a disc of metal which is reformed into a cylinder with an integral end. To this cylinder, an end is seamed to close the can. The operation of reforming sheet metal without changing the metal thickness is called "drawing and re-drawing". Alternatively the drawn can may be passed through circular dies to thin or 'iron' the walls. Drawn and ironed cans, referred to as "DWI" or "D&I" cans, are particularly suited to making large volumes of cans of the same basic specification where the height is greater than the container diameter.

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Note added at 10 mins (2011-09-23 15:13:21 GMT)
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Sorry it should be القواعد only!