I believe the problem is that you don't know the difference between the two, right?
A search will define the difference between the two & then you would know. You could ask someone what the difference is, but then the question begs to be asked,
"How is it that you did not take the time to ask the people you were buying the headers from what the difference is, isn't that part of their job?
It has to do with if the plug holes are drilled straight into the heads, or at an angle.