This is a replacement thermostatic cartridge for the below selection of Aqualisa showers: - Classic 200 - Aquavalve 600 - Aquavalve 605 - Aquavalve 609/Colt Concealed - Dream - Aquavalve 700 - Shiraz - Aquastream Mk3 - Aquamixa - Axis Thermo - Quartz Thermo - Opto Thermo - Hydramax Concealed Range These cartridges are suitable for use on low pressure, high pressure and combi boiler systems and being thermostatic they ensure that water temperatures are kept at a constant level. The bonus of this being that you won't be shot with icy cold or boiling hot water, a brilliant feature for households with vulnerable people.