Nút chặn ống silicon (Silicon tube stopper)

Some time ago I found a silicon tube stopper on thingiverse - but it didn't fit tubes sold here (those are 16mm OD of the screw)

 So I made a new one - but it didn't seal well

And then I designed this model, it has space at the bottom (or is it top) for a gasket or an o-ring.

Instructions: 

1. print the main part in your favorite filament and the gasket in a flexible filament.
2. Push the gasket (or o-ring) past the screw threads to the end of the stopper
3. Hope this seals the tube properly

I've added a version designed to be printed in flex material and be its own gasket