Yamaha - Hose Nipple Cooling System Hose Connector 6E5-45378-00-00. Overview. On older Yamaha outboards, little fittings like this can be the difference between a clean cooling system service and a leak that keeps coming back. This Yamaha Hose Nipple provides the threaded connection point that lets cooling hoses seat properly and keep water moving where it belongs. When these fittings corrode, clog, or get damaged during teardown, replacing them with the right OEM part saves a lot of headaches.