Oceans Wonders Coral Frag Plugs are perfect for the propagation or fragging of hard and soft branching corals such as Acropora, Birdsnest, Montipora, Kenya Trees, Xenia, ect. They have a 3/4" crown with a 7/16" base and fit perfectly into standard eggcrate or into small cracks or crevices in live rock. They are made from a fused special grade bright white 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