The first riser is 6".
I bought some 3" also (don't really know why I did after I bought it
should have just got 4" instead), but, I would rather use 4", so, I may have to get some tomorrow. I can always find a use for the 3".
I saw the pictures of the Beckett skimmer in action. Looks like it is working great now.
What are you going to do with your "old" skimmer?