| 摘要 |
A piston has a piston head made of ceramics, and includes a ceramic piston head having a male rounded thread portion at the outer periphery thereof, a metal piston body having a depression in the top portion for receiving the piston head, and a female rounded thread at the inner periphery of the depression for mating with the male thread portion. A rotation restraint member is provided between the male thread portion and the female thread portion for restraining the piston head from turning with respect to the piston body. The ratio of the height of the thread to the pitch preferably is from 1/4 to 1/2.
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