A spare male foster fitting was used to supply some basic dimensions. Chopped off a small piece of acetal rod.
Faced the acetal in the Taig and added a small bevel.
Cut a couple grooves for o-rings. This is all just quick freehand so far.
Need to get the other end to about this diameter.
A really small homemade parting tool did the trick.
A few comparisons to the foster part showed where to make some additional relief cuts.
Two green o-rings will help me find the plug when I set it down on a dark floor.