I need to build a milk stand. I have looked over different web sites and have gotten alot of info. Enough to get it all built in my head.The only thing I need is the opening for the neck. Once it is closed, what should that opening be? I have seen it to be four inches, but that seems a bit large for my nigerian drawf's neck.I see folks on here who talk about milking and would love to know ya'lls size opening. Thanks in advance.