Help With Bottle Cap Thread Design

I'm trying to design and print parts that can screw onto the top of the bottle, just like the cap does. This is one of the cheap, thin plastic water bottles with a cap that is about half of the size of a "standard" size bottle cap. I've looked all over for thread specs on these types of caps but haven't found anything really helpful. I've gotten pretty close by trial and much error but the piece I made screws on a little crooked and does not feel mechanically sound. One thing I have noticed about this thread type is that it is not a singe continuous revolution, its three separate half revolutions. Does anyone here know how to make this thread type correctly and or what the actual thread type/size is?

Soda Bottle Threads

Poor Mans Open SCAD screw Library

Standoff MotherBoard M4 - M3 4mm

Maryland metrics thread data charts

The internet is filled with samples and data charts.

Most likely the thread you are look for has already been done Modeling Threads.

I've been able to find plenty of info for soda bottle threads and other common thread types. The hard part is that this is not a soda bottle or anything that resembles common thread types. I think I have the wrong pitch size and need three separate half revolution threads, 120 degrees apart.

I would cut the original caps with a band saw or other means so as to be able to get to the threads in the cap to measure them with a caliper. As you say, they are not full helix they are curved and angled sections that lock between the same on the bottle side. You need to measure what is there and recreate it.. Sorry I can't really help, and good luck!

Another option would be to utilize the existing cap to attach whatever it is you want on the bottle to it.. Not helpful for mass production but if this is a one or 2 off..

Alright, I got it figured out now. The threads on this particular bottle neck/cap are 23.5 mm in diameter and 6 mm in pitch, three 1/2 revolutions, spaced 120 degrees apart. I started the thread pattern 1.5 mm in from the edge of the cap that I made. I came up with this by measuring the threads on the bottle neck since I don't really have a way to cut one of the caps in half to take measurements from a cross section, although this would be the preferred method. Thanks for the help and input!
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