I am not an expert but generally the US ones are either Aluminum (older versions) or Stainless in the newer versions. THey are generally curved to fit to your body better and match the canteen they fit in. The Brit pattern was "pattern 58" and they are more oblong and rounded if that makes sense. Here is a pic of the british version http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2180112417&category=588 The US cup looks like this in the aluminum version http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2180368462&category=4721 The differient letters you have found probably denote the company that actually made them. Hope that helps. akraven