Just done a search on eBay for Daihatsu Cuore Water Sensor and 3 came back in the search results. No specs of the diameter on any of them, but you could always ask the seller that question. Also check the plug connectors to make sure they are correct for your wiring. Worth a shot. Also worth contacting IM (International Motors) selling on EBay as Impartsb46 as these are the official UK parts suppliers for Daihatsu, Mitsubishi, Subaru UK dealerships, and you may get this part cheaper than going through the actual dealerships.