These gaskets are used for boiler hand hole and tube cap assemblies. They are available in round, oval, obround, square, pear and diamond shapes. Please note Style T gaskets rely on internal pressure in the boiler to properly seat the gasket. This means, when a hydrostatic test is performed on the gasket, the pressure exerted against the plate will further compress the gasket and it is necessary to tighten each nut to compensate for the additional compression of the gasket under load.