MGDuff B77 Backing pad for ZD77, AD77 and MD77 bolt-on anodes. Features Designed to stop the back of the anode from wasting away, and possibly causing the anode fixings to come loose Provides a barrier to help protect GRP hulls from alkalinity that can be produced as part of the cathodic protection process Keep water from behind the anode so that only the front is eaten away Reduces marks when fitting on fibreglass boats Anode backing sheets should be replaced with every new anode.