neck/cap size

Does anyone know the neck ring size for bottles in different regions of the world? I have moved to Fiji to work for a few years and have discovered that their beer is not so great and have had to get back to home brewing. Since my bottles are in storage I had to drink several cases of Fiji Gold in order to get some bottles. They seem to fit but I have poor carbonation in my bottles. I did a primary for two weeks and then bottled using the amount of sugar that came in the kit so I am sure it isn't that. Plus, I did make sure to stir very well. The first culprit that I can think of is that the neck ring size in the Pacific might be smaller than in the US where my caps are from. Any Aussies or New Zealanders out there that might know thiis?