I was trying to find out just what the thread specifications are for soft drink bottle tops, as I wanted to machine some parts which would screw on to the top of them. In the UK (and probably elsewhere, but I don't know if the threads are the same), we currently have the two shown in the photos below. One has just over three turns, the other just under two. The one with fewer threads seems to be a recent introduction over the past 3-4 years or so.
Here are a couple of examples of the threads. On the left is a 600mL 7-UP, on the right a 500mL Diet Coke.
A friend who works at Carlsberg Breweries asked their packaging manager, who very kindly replied with info on exactly what the threads are!
The threads are standardised by the International Society of Beverage Technologists (ISBT), and a list of lots of thread specs is available at http://www.threadspecs.com/threadspecs-downloads.asp. Warning: the thread specs are extremely detailed!
The thread on the left is called PCO1810 (also PCO28) and is the older style. The thread spec is available here (PDF file). Outside diameter is 27.43mm and pitch is 3.18mm.
The thread on the right is called PCO1881 and is the newer style - lightweight and lower profile. The thread spec is available here (PDF file). Outside diameter is 27.4mm and pitch is 2.7mm.
(Both the above PDFs were obtained from ISBT's page at http://www.threadspecs.com/threadspecs-downloads.asp and are mirrored here for convenience.)
Based on these, I was able to thread the parts I needed and got a really nice smooth fit on the thread. Although the thread profile is specified in detail in the PDFs (root and tip radius etc), I just used a V-threading tool and it fitted fine.
Many thanks to Steen Vesborg and Håkon Langen at Carlsberg Breweries for their help!
Some more keywords if Google sees this: soda bottle, drinks bottle, pop bottle, thread size, cap size, top size, thread specification dimensions, carbonated soft drink, CSD.