This is a rack for scrub daddy sponges, designed to be screwed into the bottom of a shelf. It uses 8mm rods.

 You can use standard linear rods,  however I recommend using stainless steel rods or coating the linear rods as otherwise they will rust.

You can cut the rods to any length you want to accommodate your needs.

I used 3x20 mm wood screws, but you can use any  countersunk screws you want as long as they aren’t thicker than 4mm, otherwise they won’t fit.