Made these for my parents who refuse to waste a drop of ginger ale or club soda when mixing their high balls.  Printed from PLA and has a groove to accept a 55mm OD x 48.8mm ID x  3.1mm nitrile O-ring as a gasket.  Not guaranteed to stop the contents from going flat, but does help.  At least it prevents spills. Sourced the O-rings from Amazon here.

For standard aluminum 12oz beverage cans in the USA.  Will probably fit different sizes as the tops seem to be all the same dimensions for different volumes.