"Bathtub" That's what it is commonly reffered to. I like them because they keep excess heat from the oil splash from overheating the manifold. I have run into M motor problems that the intake wouldn't clear it and pushed it down so port holes for intake and water ports wouldn't line up. If yours clears, use a Flepro set (not cheap) and an optional pre siliconed piece is available. Almost all of the Felpro sets have a tube of black rtv for water ports and as for intake ports, it's a matter of personal preference as to whether you put the rtv around the intake ports (go sparingly). If your manifold does not clear, "singles" can be used but be weary of extra heat on the bottom side of the manifold which transfers to the carb and so on.