An exhaust gas pressure tube assembly and a method for making the tube are disclosed. The assembly includes a keyed washer having a concave conical opening and an exhaust gas pressure tube having an open end for attachment to the boss. The assembly method includes positioning the washer adjacent the boss attachment open end of the pressure tube such that the concave conical opening of the washer faces the open end. A tool is positioned against a washer side and a mandrel having a conical outer surface is then inserted into the open end, causing the open end to be flared against the opening of the washer. The surface of the concave conical opening of the washer may be either smooth or knurled. If the surface is smooth, the mandrel is retained in its flaring position and a brazing or similar procedure to form a strong and gas-tight seal.