Marine Manhole Cover Type B: is good for applications where frequent access is not required. It is ideal for tank top cover, bulkhead access, fuel and water tank access.it will be made of high strength steel. It is fixed on the flat positions on the hold bottom, deck and bulkhead. There are Type A,B,C,D&E. The shape can be round, oval, square. *Manhole Cover Type B is also called as Marine Flush Manhole Cover. Main Material: Cover: Carbon Steel Coaming: Carbon Steel Seal Ring: NBR Bolt, Nut, Washer: Stainless Steel, Caron Steel , Copper.