Volvo Penta Zinc Pencil Anode | Martyr CM838929Z Aluminum sacrificial anode reduces the corrosive affects on a marine engine. Volvo Penta pencil anode Zinc anode for salt water applications 7/16 -14 UNC male thread and M8 female thread 1.7 in. length 0.7 in. diameter Replaces Volvo Penta 838929 For aluminum see p/n CM838929A For magnesium see p/n CM838929M