This stainless steel blockoff plate is sandwiched between 2 gaskets to separate (block) the coolant in the manifold from the exhaust water which exits through the riser on freshwater (closed system) cooled applications or applications where the water goes through the manifold before entering the engine.
"WARNING: This product can expose you to chemicals including Carbon Black, which is known to the State of California to cause cancer and birth defects or other reproductive harm. For more information go to www.P65Warnings.ca.gov."
www.P65Warnings.ca.gov