The Mira 903. 33 Excel Thermostatic Shower Cartridge Assembly, also known as the Select Mk1 is suitable for high and low pressure installations. This spare part replaces the older models, 903. 27 (Low Pressure, yellow hub) and 903. 28 (High Pressure, green hub), which are both now discontinued. This product is for showers made prior to 2003, for Mira Excel models after 2003, please see the Mira 451. 71 thermostatic cartridge assembly instead.