(57) A front fork blank of the single unit type is manufactured from a center butted tube,
the wall thickness of its middle portion exceeding that of both end portions of the
tube, as a starting material. The center butted tube is produced by a known machine
including a mandrel and a die. The center butted tube is bent at two positions with
the right angle to form a tubular fork. The tubular fork is set in a sectional die
which has a concave recess corresponding to a protuberant socket, and subjected to
the known oil hydraulic bulge-forming process in order to bulge-form the socket at
the middle of the top of the tubular fork. The socket is opened to receive a stem
(Fig. 13).
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