Hi Joralin. I use round metal beads I found in the sewing area at Walmart. Also called "spacer" beads. They are small enough to fit through the hole for the pins. But larger beads could be used if you fish the strings out through the sound hole and tie the bead on. I'm afraid I don't remember what size the are. They look to be 4mm dia. sitting on a ruler. (Measuring with the hole sides facing the ruler.) I think a pack of 50 cost $1.75 USD about 4 years ago.
I also got a pack of 5mm(?) beads with ridges (fluted) sides. They were a very snug fit to go through the Kanile'a holes.
I had some plastic beads. But they broke when I tuned up my uke and strummed it fairly hard a few days later. With a pretty loud pop! For a moment, I was afraid I had broken something inside the uke.
Romero strings come with plastic square beads with G, C, E. A on the sides. Nice looking, but they break very easily. Tried them twice and each time at least one string broke a bead under tension. And they were fluorocarbon strings. I'd be leery of glass, wood or seed beads.
Make sure the bead has a large enough diameter hole that your thickest string will go through. I think most have a 1mm hole.
Any sewing store or art & craft store should sell similar metal beads. Mine are similar to these:
https://www.walmart.com/ip/DIY-Craf...ead-Silver-Tone-100Pcs/857567220?from=/search
I'm sure Amazon will have them. I notice that they also have stainless steel beads. Not a bad idea if you use an Oasis type humidifier. I would prevent any oxidation or the metal. But that's really over-thinking this.