Oceans Wonders Reef Plugs are perfect for the propagation or fragging of hard and soft branching corals such as Acropora, Birdsnest, Montipora, Kenya Trees, Xenia, ect. They are bright white in color, have a 7/8" crown and fit perfectly into standard eggcrate or into small cracks or crevices in live rock. They are made from 100% Pure Caribsea reef sand. This sand is a natural calcium based sand which has been shown to speed the spread of coralline algae growth and corals on the plugs. Each package has detailed usage instructions on the back.