All TrojanUVMax UV systems include a quartz sleeve, which surrounds the lamp. The quartz sleeve provides thermal protection for the UV lamp and protects it from possible water damage. The quartz material used in VIQUA quartz sleeves are a 100% fused silica which lend to the sleeve's high transmittance. A high transmittance is important as the UV light must travel through the sleeve to get to the water. There are a variety of quartz sleeve designs, depending on the system that they are being used in. All VIQUA sleeves have been tested in order to ensure the VIQUA lamps deliver the appropriate intensity in each system that is offered. Make sure to GET GENUINE and always maintain your system with GENUINE parts from your VIQUA dealer. Systems used in: E, E+, E4, E4+ Description: Domed at one end