Engine anode (pencil), 3/8″ diameter, 2″ length, 3/8″-16 size thread. Fits a 3/8″ NPT brass head. Pencil zincs Harbor are machined from extruded rod, which has a tighter grain structure and more strength than cast parts. These anodes are used in water systems for cathodic protection of engines, heat exchangers, condensers, pipes, etc. and conform to MIL-A-18001K and MIL-DTL-18001L alloy.