What can I use to replace the bead on the umbrella?

You can use the ballpoint pen refill or wire sheath that has been filled with ink. I just used the wire sheath to make the tail beads of the entire folding umbrella. The original ones were all made of plastic and have aged. Peel off about one centimeter of wire skin, insert half of it into the umbrella rib, burn the other half with a lighter and flatten it, sew the wire skin to the umbrella surface with thread, tie a knot and tighten it, and you're done!