Cotter-pin alloy should be appropriate for the application. In most cases that means stainless steel. For instance, for a submerged propeller application, use 316 alloy. On-deck applications can use 18-8-series stainless steel; however, if the pin will be covered by tape or a chafe guard, crevice corrosion remains a concern, again making 316 the preferred choice. Unless specified by an equipment manufacturer, under no circumstances choose brass cotter pins. Brass is comparatively soft, prone to dezincification when used in in the marine environment and galvanically incompatible with aluminum.