Oceans Wonders Coral Frag Disks are perfect for the propagation or fragging of hard and soft branching corals such as Acropora, Birdsnest, Montipora, Kenya Trees, Xenia, ect. They are 3" in diameter and 5/16" thick. 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 disks.