Typically used on the rudder shaft in pairs. One above the deck is flat on both sides and prevents the rudder head from wearing the fiberglass. One below the hull is beveled on one side. The beveled side faces down, toward the rudder. Sealant (the high strength adhesive / sealant shown below) is applied inside the bevel and helps seal the rudder shaft where it enters the rudder blade.
The price indicated above is for a pair of washers.