I finally made up my mind to underwrap the butt guide on the spiral rod I am buiding, but I also found out that I should of used D thread for the under wrap, cause when I went to wrap the guide, the A thread that I was using kept like getting inbetween the A thread on the underwrap, and I couldn't move the threads into place without disturbing the underwrap threads. What I am concerned about know is the height of the butt guide now to the other guides, the guides do as follows, butt guide 6mm, then the 5mm then 2- 4mm's, then 3.5's all the way to the #6 tip. would it hinder the flow of the cast,(pitching).

There is no need to underwrap it, but it's not really going to hurt anything if you do. To use A over A, simply apply a coat of CP or epoxy on the underwrap and then overwrap on top of that.

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You really didn't change the height of the guide at all by putting an underwrap on. So I don't see how it could affect the line flow.

I put a very light coat of epoxy on the underwrap, I really did it just for the looks of it, so now I''l have to wait till it all gets done to see how it all goes.

I've not been able to use a larger size underwrap thread. In my experience, if you underwrap with D, the A overwrap will want to lay in the grooves of the larger threads, and no amount of burnishing will keep the underwrap color from showing through. I mistakenly bought a spool of # 60 Madiera thread (blue spool base) I didn't immediately notice the difference in sizes. I tried to wrap it over the heavier standard #40 Madiera and it looked like crap. I have found if I use enough tension on the underwrap, I rarely have a problem packing the occasional gap in the overwrap. I never use any epoxy or CP until the entire rod is complete. I've never thought of doing that. I may try it if I ever have a problem with thread packing.

The underwrap thread should be smaller than the overwrap thread.