Drain plugs for boat, canoe and kayak bulkheads. The plug unscrews but is held captive to prevent it being lost. Stainless steel screws are included.
These keep the buoyancy tanks airtight and should be unscrewed to allow air circulation when the vessel is not in use. Failure to unscrew them can result in the tank exploding if left for a long time in a sunny position.
If you want to store small items in your tanks, you will need larger hatches.