How do I correctly dimension a thread in a part drawing?

I'm making a part drawing for a screw on cap to a container and don't know how to dimension the thread in the part drawing.

2 Answers

Start by using a standard thread.
For example, using 1/2 - 12 UNC 2B on a drawing is enough to "dimension" a thread. Granted it is a thread callout, rather than dimensions, but the rest of the information comes from the thread standards.

Caps used on containers can use a number of different threads. Plastic threads, glass threads, buttress threads, rolled threads, multi-start threads.... Lots of standard threads already exist. What thread are standard are you using?

Attached is an image of a cap I designed with a 6-4 7°/45° 2B American National Buttress Thread.
Modeling the thread was needed for 3D printing, and fit testing with an existing object. If the part were going straight to production, I'd have skipped modeling the thread, and just applied a callout on the drawing.

Typically, dependent on the thread... you will want to dimension the diameter at the top of the threads, the diameter at the base (the cylinder the threads were built upon) the pitch, the lead and the included angle of the thread.

If working to DIN or some standard, note that as well.