Mounting frags to your rock work has never been easier with these rock holders! Many people have trouble finding the right place on the rocks and worry if their corals will fall out. These rock holders allow for flexible placement anywhere on your rock work. Simply slide your frag plug into the opening, and insert the holder into your rock work. These also allow you to change the placement of your corals whenever you please. Standard Dimensions: H: 1.6" Opening: 0.4" - 0.5”, stem is 5/32” (4mm) in diameter 0.5 inch Dimensions: H: 1.6" Opening: 0.5" - 0.6”, stem is 5/32” (4mm) in diameter 0.6 inch Dimensions: H: 1.6" Opening: 0.6" - 0.7”, stem is 5/32” (4mm) in diameter Each holder is made from PETG high-quality filament. PETG is safe for food containers and tools used for food consumption. Patent Pending