| 摘要 |
Fastening bolts (70) fasten a first head member (61), a first cylinder (51), and a second head member (62). The first head member (61) is disposed on one axial-direction end side of the first cylinder (51). Protective grooves (80) are provided in the end face of the first head member (61) that touches the first cylinder (51). The protective grooves (80) are formed nearer to the center of the first cylinder (51) than the fastening bolts (70), and the groove width (W) of the protective grooves (80) is less than the groove depth (D). |
