After spending hours upon hours building a handle, wrapping guides, spinning a decorative wrap, and any other time consuming tasks associated with your rod build, the last step is to apply your epoxy finish. Though it is the last step, it is definitely not the easiest step. More rod building questions are stemmed from epoxy application than any other of the necessary steps.
There are many different threads that can be used when building a rod. They vary from color treated (thread that has already been treated with color preserver), regular nylon, metallic, and even polyester.
Many people ask about which thread needs color preserver and which ones do not, and the answer is any nylon or polyester thread needs color preserver. Metallic threads do not need color preserver.
With that being said, it never hurts to use color preserver on anything if you are questioning whether you need it. It will not hurt either way.