Quicksilver 31640Q4 Aluminum Trim Tab Anode - Mercury or Mariner Outboards and MerCruiser Stern Drives Helps protect gear case housing from corrosion as it provides hydrodynamic trim force to your outboard and stern drive to aid steering Produced to Meet Mercury marine original equipment Manufacturer specifications to best protect your Mercury Mariner or force outboard Each anode is designed for fast and easy replacement with common tools remembering to check propeller Clearance prior to Operation Inspect anodes periodically for best protection and replace when seeing signs of corrosion or pitting to help keep your maintenance costs down These cast aluminum anodes meet or exceed mil-spec MIL-A-24779(SH) providing longer lasting protection than zinc anodes and are for use in fresh or salt water