| 摘要 |
A piston with a built-in seal comprises a piston body (121) formed of a metal press-formed part and axially movably disposed in a clutch cylinder (110) and seal lips (122, 123) formed integrally with the piston body (121). A through tubular guide projection (124) is formed on the piston body (121). A return spring (150) for biasing the piston body (121) toward the pressurizing chamber (A) side is held on the guide projection (124). Since the press-formed through tubular guide projection (124) is higher in projecting height than the bottomed tubular one, the length over which the return spring (150) is held is longer. A pressurizing chamber (A) is prevented from being opened by the guide projection (124).
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