If it is impeding flow, it's impeding just enough cause this thing is working really, really well.The head won't be staying on. I was at work and happened to have this screw so decided to coil it up for a quick test. I had no access to tools. I have it lined up height wise where it should touch but I'll be getting rid of the head shortly.
BTW, I insulated the screw with just enough cotton to do the trick.
Is there such thing as a galvinized screw? If so this is worrysome.