Summary

Printed with a NinjaFlex, but any flexible should do.

Instructions

Design file is included, you could make the base wider/taller, but this seems to be the bare minimum. I'll update it if this version breaks and I need to print replacements, make sure to print hot to get additional interlayer adhesion as otherwise it may be possible to separate the plug from the base disc.

Important dimensions to consider if you remake this, make the plug part 1mm thicker than the diameter of the hole. 2mm is too difficult to get in. Also the cone really helps get the part in.

Printrbot Metal Plus Replacement Rubber Feet