I bought slide stop screw as a replacement for the old one, simply because the old one tarnished a lot and new one is not expensive.
However, when I replaced it, it turns out that this new one touches the third valve slide.
My 6310z is second hand instrument so there is a posibility that something is bent for the part of the millimeter, although I don't see it and the old screw works as it should (it doesn't scratch the third valve slide as this one).