EN 417 is a European specification concerning non-refillable metallic cartridges for liquefied petroleum gases. More colloquially it is used to refer to the threaded 7/16 NS (Lindal Valve) on disposable butane and/or butane/propane mix cartridges used for backpacking stoves such as those supplied by Epigas (Coleman), GoSystem, Primus, Brunton, Jetboil, Snow Peak, etc.
http://www.standardsdirect.org/standards/standards1/StandardsCatalogue24_view_13911.html
http://www.lindalgroup.com/en.product.php?id=6