Bottle cap thread calculator

This tool calculates the thread specifications of bottle caps for modelling in CAD programs such as Fusion 360.

This is intended for use with bottles that conform to ASTM D2911, also known as "GPI" or "SPI" thread finishes.

(While ASTM charges $60 for the spec, the important parts can be found freely online.)

This assumes that you are modelling the thread by creating a coil with a triangular cross section, then cutting the tip of the triangle off with a cylindrical hole.


Neck finish specifications
0.2 mm is suggested
Cap thread parameters
Used to flatten the tip of the thread


How to identify the neck finish on a bottle

How to model a threaded cap in Fusion 360

Helix angle calcuation

Preset calculation spreadsheet