9. A METHOD OF FORMING THRUST PORTS IN THE END PORTION OF A HOLLOW CHAMBER, WHICH COMPRISES SUCCESSIVELY PUNCHING SAID END PORTION TO PROVIDE A PLURALITY OF OPENINGS THERETHROUGH, INDENTING SAID END PORTION OUTWARDLY OF SAID OPENINGS TO PROVIDE ANNULAR INDENTED END PORTION SEGMENTS, AND HEADING SAID END PORTION AND THE INDENTED SEGMENTS TO PROVIDE ANNULAR THICKENED COLLAR PORTIONS SURROUNDING SAID OPENINGS, THEREBY PRODUCING THRUST PORTS OF SUFFICIENT STRENGTH AS TO RENDER UNNECESSARY WELDING OR OTHERWISE ATTACHING COLLAR MEANS.

10. A METHOD OF FORMING A HOLLOW CHAMBER WITH AN INTEGRAL SKIRT PORTION THEREON, WHICH COMPRISES DRAWING A CUP-SHAPE TO PRODUCE AN ELONGATED SHAPE HAVING A REDUCED THICKNESS BODY PORTION AND AN INTEGRAL ANNULAR THICKENED PORTION, SHAPING SAID THICKENED PORTION TO PRO-