The myREEF-FRAG RACK features 8 holes with a magnet, making it ideal for holding individual coral fragments. Each hole, measuring 15 mm in diameter, includes a silicone insert to securely hold the frag plugs. These holes are compatible with most standard frag plugs on the market. All materials, including the magnet, are safe for use in saltwater aquariums. The powerful magnet supports glass thicknesses of up to 12 mm, ensuring a firm and stable hold.