This is simply a deck cap for a pool fence. The top diameter is 36mm and diameter of inner (bottom) cylinder is 26mm and height of 17.4mm If re-size is needed just use a tool like cura to re-size and the inner/bottom cylinder will re-size as needed.

Update 4/25/2017 I have uploaded a new version of the pool cap with the filename cap-chamfered.stl. This one was created to save on wasted support material and so the top is completely flat. Print this cap-chamfered stl file with the top part down on the print bed. I also added a small slot on the bottom where you can now press in a nickel to help add weight.