Technical drawings pens are held upright and have a circular tip that gives a specific line width based on the diameter of the tip.

If you're inking your drawings, you probably don't need to worry all that much about the exact line width and consistency of your pencil work.

N.b. I don't ink my drawings. I've used drafting pens a couple times to experiment, but it's not part of my regular workflow.

https://www.jetpens.com/blog/The-Best-Technical-Drawing-Pens

This will be an excellent addition to the list. Curve lines are a challenge I have yet to tackle in depth.

> lines a consistent thickness

A "ruling pen" would help. It's like a fountain pen where you can adjust the width of the ink.

https://en.wikipedia.org/wiki/Ruling_pen