Ancor Vinyl Step-Down Butt Connectors are used to join a pair of conductors to a third, all of the same size or two conductors of different sizes. Ancor's Marine Grade terminals differ from automotive terminals by being designed specifically for the harsh marine environment. The barrels are designed to tightly grip the wire with the least effort. Tinned copper offers the least electrical resistance while providing the most corrosion protection. UL 486C.