PROBLEM TO BE SOLVED: To provide a joint for core capable of preventing breakage caused by stress generated by force received from a coupling.;SOLUTION: The joint 1 for core is provided with large-diameter parts 1a, 2a and small-diameter parts 1b, 2b in one end. The large-diameter parts 1a, 2a are housed into a groove 3c in a coupling 3 with which the core is connected to a cylinder for pulling out the core. The small-diameter parts 1b, 2b are joints 1, 2 for core passing through the holes 3a, 3b of the coupling 3. Stress relaxation grooves 1d, 2d are formed in the small-diameter parts 1b, 2b of the joints 1, 2 for a core.;COPYRIGHT: (C)2009,JPO&INPIT
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