3-3\/4" Rudder\/Trim Tab Anode – ZincAluminum trim tab or rudder anode with 2 halves and stainless steel hardware. Nuts are pressed into the casting.Performance Metals Navalloy® aluminum anodes are manufactured to the military specification MIL-DTL 24779 and are suitable for use in all water types- salt, brackish, or fresh.The anode includes the exclusive, patented “red spot” wear indicator.