The Evinrude Johnson core plug part number 303405 is a cupped plug, sometimes referred to as a welch plug or dish plug. It's designed to seal engine passages, preventing leaks of water or coolant, and can also help prevent freeze damage. These plugs are typically used in marine engines, like Evinrude and Johnson outboards, to close off passages within the engine block Here's a more detailed breakdown: Cupped/Welch/Dish Plug: This type of core plug has a shallow cup or dish shape, which allows it to expand and seal the hole when driven into place Function The Primary purpose of a core plug is to seal a passage or hole in the engine Application Core Plugs like 303405 are commonly found in outboard engines like Evinrude and Johnson to Seal Coolant or water passages Prevention These Plugs can also help protect against freeze damage by sealing off coolant passages.
