Marine manhole cover is a general term for the cover plate with sealing performance and its fixed accessories installed on the manhole. According to the condition of the sealing plate, the manhole cover is provided with the raised sealing plate at the periphery of the manhole; a flat manhole cover with only one circle of flat seat plate at the periphery and fastened by stud bolts; the edge is provided with a sunken coaming plate, and the buried manhole cover is not protruding from the surface of the plate. according to its shape can be divided into oblong and circular, of which oblong manhole cover is more widely used. According to its tightness can be divided into oil-tight and watertight, the difference between the two lies in the material of the sealing gasket, oil tight should use oil-resistant rubber, watertight should use sea-resistant (light) water rubber. This article will introduce the C type recessed manhole cover to help you choose the right product.