PURPOSE: To firmly secure a sleeve to a nipple by a method wherein the sleeve provided with a conical bottom part being inclined inwardly and a hole formed in the central part thereof is engaged with the outer periphery of the nipple, and the size of the outer periphery of the bottom part of the sleeve is reduced to caulk the inner surface of the hole to the sleeve securing part of the nipple.

CONSTITUTION: A press work is applied on a thin steel sheet to form a bottom part 2 of a sleeve 1, which is inclined inwardly of the sleeve 2, and a hole 3 is formed at the central part thereof. The sleeve 1 is positioned on the outer periphery of a nipple 5 such that an inner surface 4 of the hole 3 is positioned facing a sleeve securing part 6 of the nipple 5. With this state, the size of the outer periphery of the bottom part of the sleeve 1 is reduced to move the center side of the bottom part 2 from the inner side of the sleeve to the outer side thereof to reduce the diameter of the hole 3. This method firmly secures the sleeve 1 to the nipple 5.