This is just the replacement magnesium anode. Magnesium engine anodes provide superb corrosion protection for marine engines that operate in fresh water. Each has a steel core to reinforce the anode until completely consumed. Threads are measured by NPT standards (National Pipe Thread).
Note: NPT sizes do not refer to any physical dimension. Determine your NPT size here.
Fresh Water Use Only
E-2Z-M Magnesium Anode Shown Above