bairdco
I live for the CABE
A cork and a wood dowel.
Pretty common. Colson bikes always have corks in the tubes inside the bottom bracket shell.
I think it's because they're dipped in solvents that would corrode the tubes from the inside out.
And a lot of old bikes were dipped in paint, so corks would keep the tubes from filling up.
I've found a colson build sheet in a fork tube, money in handlebars, an alloy fluted bmx seatpost in a seat tube, which probably got dropped in and stuck, then another seatpost on top of it.
Found an original receipt with the owners name and address in an old monark handlebars, and some 22 bullets rattling around inside of some bars.