Advanced Aquaculture Ceramic Reef Plugs are specially designed to fit nicely into a small crevice or hole in your live rock as well as eggcrate. Reef plugs are designed primarily to support Acropora, Montipora Digitata and other thin branching species of coral. The top is about 1" in diameter and many will have a small divot at the top to hold a pool of glue where your frag can rest. Ceramic plugs require no curing and will not leach anything into your water.