For stopping airflow in my dust sucking vacuum system. This you can use at the end of the 40mm pipe. The old version is still available in the SketchUp file.
Update: Complete redesign again because I wanted the lid to stay closed, so I added a spring.
Update: Complete redesign due to overhang mistakes. :)
Print and mount. You may have to file a bit on the "pipe". It's very tight fit on the 40mm pipe.