You can buy rubber plugs at Lowes in the fasteners section in those sets of drawers. All kinds of stuff in those drawers. I purchased some larger grommets from McMaster Carr recently that has an oversized hole and for thicker panels. The size chart is handy in determining the size needed. Keep in mind that if you need a smaller outside diameter but need the ID to be larger or the panel thickness to be larger you can always make a cut thru the grommet and remove a small section to fit a smaller hole. But if you know that Bill has them at Allison and it's exactly what you need then it's worth the extra couple bucks.