Here is the skagit head that launched this system! Available in sizes that match well with 3wt single hand rods all they way up to huge 8-9wt spey rods. These heads require the use of a running line. Check my link for OPST lazar line, its the best one out there.
I use a 150 grain on my 4wt glass rod. The 225 on my 6wt glass rod. And currently am running a 400 on my 8wt switch rod