Sierra 18-6012 Mercruiser Zinc Trim Tab AnodeSierra high-quality replacement anode for Mercruiser Stern Drives. For Use On R/MR/Alpha One (Sterndrive & Transom Assembly 1983-90) And Prior Drives, Alpha One, Gen II (1991 & up). Material: Zinc; Will not work with Black Max or other high rake propellers; Interchangeable with: GLM; 12740; Mercruiser Stern Drive; 34127A1; 34127T2; 34127A2; 34127; 34127T1;