Martyr Zinc Pencils for inboard and stern drive engines. The sacrificial pure zinc rod prevents galvanic corrosion on internal engine parts. Anodes are sold with a brass end plug. UNC size anode thread screws into the plug. NPT size plug thread screws into engines, heat exchangers, pipes, condensers, water cooling jackets, etc.

Zinc anodes should be checked periodically and replaced when only 1/3 of zinc rod remains.