Fits size 30.25 x 12.5 x 12.75. The 20 gallon tank divider is suitable for 20 gallon long tanks. It’s made from a solid material with adjustable sidebars. The clips are used on the rim of the tank for added stability. The divider does NOT work in rimless tanks. The divider works best in a tank with substrate; it may not be suitable for bare bottom tanks. It comes with a full instruction sheet and video link to help with installation. Things to note before buying: These dividers are not flimsy and have been made with Betta Fish in mind. You will require filtration in each section to help with water flow. **Sale is tank divider only. This listing is for a pack of 3 dividers. The pictures of the tank are a representation of how a tank can look using two or three dividers. * All Betta fish may not be suited to living in a divided tank.