This is a metal pulley for a Magnum boat lift AMS motors. The dimensions for the pulley are:
Diameter: - 5 1/4", 6", 7", 8", 10", or 10.5"
Bore Hole Diameter - 3/4"
See the Specifications Tab for Boatlift models.
When replacing pullies, it is a good idea to inspect the belt as well to determine whether or not they need to be replaced. Your goal is to keep the pulleys turning with as little friction as possible.