These styles are designed for boiler manhole cover assemblies. They are usually round, obround or oval shape, depending of course , upon the manhole plate configuration. Style MC gaskets have pre-formed inner and/or outer rings made of spiral windings. This centering guide permits the gasket to assume its correct position and to compensate for inequalities in plate contours and fillets in cold-pressed plates as well as to prevent shouldering and pinching caused by radial misplacement. Style MCS gaskets are manufactured with a solid metal inner and/or outer ring which also prevents over compression of the gasket in high pressure systems.