| 摘要 |
An external helicoid thread comprises a helicoid thread composed of a first ridge whose both flanks are formed at a first flank angle, and a helicoid thread composed of second ridge whose both flanks are formed at a second flank angle, which is different from the first flank angle; and an internal helicoid thread is kept in screwed-state engagement with the external helicoid thread. In a lens barrel obtained using a connection based on such helicoid threads, the connection provided by these helicoid threads can thereby remain secured even if a sudden outside force is applied to the lens barrel.
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