I have yet to handle, much less build a rod with an extension handle. I picture that a length of handle telescopes out of the butt. How exactly does an extension handle work? Is this a 2-piece blank? What additional building concerns are there? Thanks.

I have one on my G.Loomis Flipping stick. It works like this.
There's a larger diameter butt section from butt grip to about
8" above fore grip. Then theres a smaller diameter upper
rod section that slips up and down through the larger butt
section. Kinda like on a radio attenna. You pull it up to until
it extends as far as it can go. My 7'-6" rod breaks down to
about 6'-6" which is great because I can through it in the bed
of my truck with out having to worry about it jumping out.
which is why I bought it. I lost a 8' St croix Wild River that
way I!@^$!@&%&*@$%^

Good Fishing
Joe