To put it another way, I have two Nato Osprey canteens and only one Nato Osprey canteen fits a Crusader SS mug. As to it, the Nato plastic cup will not snap on top (as it was designed to).

My underlying question pertained to why there are size non-uniformities as to this otherwise "high-end" item, to the extent that people are purchasing relatively expensive water/cooking systems that do not, in my view, work.