Update- After selling hundreds of these, we found out this nozzle is even better than we ever figured- it also fits the US cans! This is the perfect nozzle for anyone who has multiple types of cans, or who is around people using multiple types of cans!
After a long search, we have finally located a real military issue nozzle for the Nato fuel cans. This nozzle is extra heavy duty and clamps on very securely. The gasket is cut to allow the internal vent to work properly for faster fueling, and the nozzle actually clamps from the inside and hooks into the lid for the NATO cans, then uses the level to clamp the rubber seal against the top of the spout creating a seal that is super tight and super strong. I have lifted a full 5 gallon can by one of these and swung it around with no problem. On the US metal "Blitz" style cans and the plastic Scepter cans simply insert into the opening and push the level down to expand the rubber and clamp it in. The end has a fine mesh strainer for catching any contaminates in your fuel before they reach your tank, and unscrews for easy cleaning. These nozzles are used, and some will have minor surface rust that cleans away easily, but they are all ready for hard use.
These are far, far better than the imported nozzles that were the only ones on the market for a long time.
Note that these will not fit in to the openings on vehicles with tanks for unleaded gasoline as they are too large. Should you need to use one in a vehicle configured for unleaded it should be simple enough to attach a reducer from copper pipe to the end with solder or a gasoline resistant epoxy.