Making a massive gear from scrapped zipper tabs and bottlecaps in Pakistan

[Provincial]

Amazing work.
What was/is the purpose of the partial sheet of something put in the bottom?

I believe that it was a template to check the location of the mold forms. It probably was turned several times to check the segments. It wasn't a full template because that would be too hard to remove/replace, especially if a mold segment was too far inward.