Anodes are a type of sacrificial material that protect a boat's outboard motor from galvanic corrosion. They are made of a metal that is more chemically active than the material in the engine. 
 
Anodes should be replaced when half of the anode has been lost to corrosion. 
 
Complete anode kit fits most all 1976-2005 Mercury 2.0, 2.4, 2.5, and 3.0 Liter Lower Units.

Kit includes the following to keep your gear case healthy:
1 x Trim Tab
1 x stainless bolt for Trim Tab
1 x stainless washer for Trim Tab
2 x Anodes (rectangular)
1 x stainless steel screw for Anode
1 x stainless nylon locknut for Anode
 
Contact Mike Hill at STVracer@yahoo.com