Hello, I haven't been here for a long time, thank you all.
My question is that they fill in the "but" of the sections?
I am building a blank that the sections are without padding in the part that is inserted..

thank you

Are you talking about the grip and / or reel seat? If so, you can buy arbors to take up the space, or you fabricate your own directly onto the blank using masking tape. I use the tape method.

If you are talking about putting a plug or something into the open ends of the sections, yes. Most of the time the male ends are fitted with a plug of cork or even EVA foam. It is also possible to put a dollop of Rod Bond in the open end to form a plug. This keeps the end from fracturing as it goes a bit oval during periods of high flex.

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Exactly Tom, that's what I mean,
I already had the foam thing in mind, but I'll put the rod bond in.
I have been told that there is an expansive foam with carbon fiber, but I have not found anything.
Thank you very much to everyone for your help