Thank you for the Mod but I have found a bug. When the mod is un-checked or uninstalled the game doesn't go back to the default setting it stays set at 20 when it should default back to the original Factorio setting.
thank you for your time

I'm not sure what you mean. When I disable or otherwise uninstall this mod it will revert the stack sizes to their defaults.

Some containers may need to receive an update (take out or put in an item) for the larger stacks to rearrange themselves to the right stack sizes but it definitely works.

Thank you for responding . I tested the mod with no other mods activated and it is working fine. It must be conflicting with another mod I have installed. Sorry about that and thank you.