These are the u-shaped component which encases the Water Panel Evaporator. Used with Aprilaire model # 35 water panel and 4277 water distribution tray for models 700, 760, 760A and Models 768. Use distribution tray model 4277 with models 560, 560A, and 568. Also see the part number 4837 maintenance kit for the models 560, 560A and 568. Or maintenance kit 4750 for the 700 series.