The WSgift 2 Pack Safe Bone White Ceramic Aquarium Decorations are perfect for any fish tank. These two pieces come in a set and are made of 100% non-toxic and food-grade ceramic that is odorless and safe for your fish. The skulls are available in a variety of colors and sizes so you can find the perfect one to match your tank. With a front hole (mouth) diameter of 1.5 inches and a back hole diameter of 2.3 inches, these ornaments can easily fit into most fish tanks.