Inspired by @flackenstein's plug.

I wanted a single piece plug. And I wanted step files instead of STL. So I got the calipers out and designed one from scratch in Fusion 360.

The Fusion 360 design is parametric, have fun changing variables.

UPDATE: A new version of this model with twist open-close functionality is available - https://www.printables.com/model/549696-eibos-cyclopes-twist-open-close-vent-plug