These gaskets are used for boiler handhole 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.