Does anyone know what the container size 4SP1 represents? Is it a 4" pot or something else? Thanks
The only meaning that I know of would be a recycling code. #4 is a category of plastics that can be recycled (though limited to a very few things) and SPI stands for the Society of Plastics Industry.
If you see this stamped in your plant containers, it means that they can be recycled as long as your municipality accepts category 4 plastics.
At least, that's my best guess with the information given. Let me know if this definition makes any sense to your application. Or not.