1.A must have filter accessories for your fish tank,these pre sponges are made from the top-quality filtration foam, safe to your fish,suit for freshwater and saltwater.<br>2.Help to trap particles and debris,and prolong the life of your filter media,provide efficient water flow with less clogging for long lasting filtration,enhance filtration.<br>3.Give your fish pet a securaty habitate! these pre-filter sponge suit for all shrimp tank owners and anyone else who has small fish in their tank.<br>4.Sponge size：approx. 8.5x5cm/3.4x2 inch cylinder.<br>5.Inside hole diamenter: approx. 2.1cm/0.8 inch<br>6.Package included: 4 pack pre-filter sponges,black.<br>7.Please note: these foam are pre filter sponges,so only have single hole.