Typically, plastic bottles use buttress threads. I Googled this and found a Solidworks model which I changed for my needs. It worked ok. The problem with the buttress thread in 3D printing is that they are not symmetrical. One side is 45 deg. The other side is 5 deg. If you can print both bottle and cap with the 45 down, this works well. If you have to print with the 5 deg down, this creates some lousey threads on the overhang. This means leaving a lot of clearance and loose threads. Standard threads are 30 deg (60 included). I have used them before when something needed to fit to a standard thread. In this application, I am printing both parts. I can make up my own threads. I created 45 degree threads since the printer likes these best. I printed these in high quality. I was able to use .005" clearance on both sides. The threads are very tight. I need .01" clearance per side in low quality. Have not tried normal. I broke the internal threads (outside piece) from the glass first. I then screwed it off. You have to run the threads up and down a few times to break any strings. Back it out, if it binds. TREAD TEST-2 HAS TWO THREAD STARTS. Solidworks: https://grabcad.com/library/45-degree-90-degree-included-3d-printed-threads-1