Question about Shelf pins

If the pins are wooden, fill the hole with wood glue. Then "shim" wooden matchsticks around the pin until it's tight. After the wood glue dries (a day or so), cut the matchsticks flush with the cabinet. If the pins are metal, fill hole with E6000 glue and cover with tape. After glue has thickened enough to hold pin, insert pin. Then tape bottom until the glue is dried.

We had that problem and solved it with a dowel rod we found to fit, then cut it in 1 inch pieces to put in the shelf holder holes. Being wooden you can carve them down if you cannot get an exact match. That is what we had to do. Make sure the fit is tight. It did work

I whittled down the wood ones that were too big so that the end fit tightly. I did not want to go with metal pins as I was worried it may wallow out the holes in my antique bookcases.

I use metal pins and find that I can put toothpicks in the hole around the pin and just bend them until they break off. No glue needed. When the shelf is in place you can't see the hole so it doesn't matter if the toothpicks aren't cut neatly.

You could also wrap the small pins with something like teflon tape.

You could fit the pins in by using a Rawlplug to help fit.

Fill in the holes with putty so the smaller ones will work.

Home Depot, Lowes, Hobby Lobby and Michaels sell dowels in all sizes. Fill the hole with glue and insert the proper sized dowel

The dowell wooden rods sectioned off will give you many hole plugs, just cut the length you need.

I agree with De and Redcatcec's advice....go with appropriate size wooden dowels readily available and hobby /craft stores or big box home improvement stores.