This is the martyr hanging grouper zinc 

MARTYR

Clamp-on Grouper Anodes

Supplements your boat's existing anodes

An excellent anodic device to supplement a vessel’s existing anode system, especially to counteract stray current from defective shore power. 

This item is ZINC 

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Martyr Grouper Style Universal Sacrificial Anode - Zinc

Material: Zinc

Dimensions: 3" Wide x 7.75" Long x 1-3/4" Thick

Fish Shaped Sacrificial Anode with 15 Ft Vinyl Coated Cable and Alligator Clip

Brand:  Canada Metal / Martyr Model #:  CMGROUPERZ Shipping Weight:  5.85 Lbs.