| 摘要 |
A piston ring is formed by annular upper and lower parts which contact one another at respective surfaces normal to the axis of the piston ring. The parts can be injection moulded from thermoplastics materials with the parts themselves having no re-entrant portions, so allowing quick and easy manufacture, but with the parts together defining re-entrant portions such as a spring-receiving recess at the inward side of the ring or a pair of spaced oil control rails at the outward side of the ring.
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