No, this is not about bags of milk.
This is about .... the Robertson screw:
I was surprised when I moved here that my house had a screwhead I had never seen before. But I shook it off and moved on. This week, I had a contractor in my house, working to fix stuff so that we can the house in the winter/spring. He ended up telling me a tale of helping his sister in Philadelphia with renovating her house. He was flummoxed by his inability to get some screws with the Robertson head and had much hate for the Phillips screw head that is most familiar to Americans:
As this figure suggests, there are many kinds of screw heads. The contractor insists that the Phillips head can easily be stripped. Well, I have stripped more than a few Robertsons.
Anyway, this is yet another example of the challenges of being an alien abroad.