How to measure the nozzle diameter?
I have found that normal measuring devices are not particularly helpful with accurately measuring nozzle diameters. But you're already off to a great start.
What is helpful is to take them somewhere that has a wide assortment of drill bits, and find which two adjacent sizes will and will not fit in the (clean) nozzle; then convert the diameters to mm (if needed), and your nozzle is larger than the small bit, but smaller than the large bit. From that, you should be able to narrow it down to a standard dimension.