SVR21 Ultra 3/4" Ceramic Disc Quarter Turn Cartridge for ART3210 Shower Valves - Clockwise close (anti-clockwise open).Total Length (including bottom seal): 85.7mmDiameter at Widest Point: 28.5mmTop Spline Diameter: 7.8mmTop Spline Teeth / Notches: 20Barrel Diameter: 23.6mmLower Thread: 27.6mmUpper Thread (closer to spline): 24mmBottom Seal Colour: Blue (for Cold Side)Close Direction: Clockwise Close (Anti-Clockwise Open)This on / off valve cartridge is used in a number of different Ultra valves and needs replacing if your shower begins to drip from the shower head or from out of the on/off handle. This is because the ceramic discs within the cartridge have become damaged and no longer create a water tight seal.If you don't know if you need the SVR21 cartridge because you don't have a code, please measure the cartridge and compare it to the technical diagram in picture 2. If you're still unsure, send us a photo of your cartridge and give some of the key measurements. To remove the old SVR21 cartridge from the valve, use a 17mm spanner (ideally a box spanner) and turn the cartridge anti-clockwise). When the cartridge is removed, check inside the valve for debris that may have found its way through the pipes and into the valve as it may have even been these little bits that have damaged the ceramic discs. Once you are happy that the valve is clear of debris, put silicone grease on the black o'ring (and preferably on the blue rubber seal at the bottom). By doing this, it will create a better long term water tight seal.Screw the new cartridge into the valve and tighten. Turn the shower on and the dripping shower should be fixed.