These are water distribution trays that distribute water evenly to all parts of the evaporation plate. They are attached to the U-shaped scale control insert, and the water distribution tray is coated with pumice inside to distribute water evenly to all parts of the tray, and this uniform water distribution ensures maximum evaporation of the humidifier. When your water distribution trays are not working or are not working well, try opening your humidifier tray, it should have mineral deposits on it, it's time to replace it! The water distribution trays have no tools, are easy to install in minutes, and fit precisely, making them a perfect replacement part. At the same time, after our investigation, our water distribution tray is also suitable for Carrier Humidifier HUMCCLBP2417-A, Trion G-105, and may also be suitable for others, as long as the size is right, maybe it is a universal part~ Not applicable for Aprilaire WB2-12