| 摘要 |
A pulley- or roller-type block is provided with a lock arrangement. The block has a casing and a rolling unit mounted in the casing for clockwise and counterclockwise rolling. The rolling unit has a circumferential ring portion including a line-bearing surface whereby. In use the line is allowed to transit partially around the rolling unit as the rolling unit passively rolls clockwise or counterclockwise in response to alternate-direction transit of the line. The lock arrangement has a line-contacting portion operative between locking and unlocked extreme positions, and an operator for operating the strand-contacting portion. Wherein, because of the risk of forming a permanent weak spot in the line under highly concentrated locking contact, either . the circumferential ring portion of the rolling unit, including the strand-bearing surface thereof, or . the strand-contacting portion of the locking arrangement is formed from the following:-ie., it is formed from a resilient material so that the compressive force on the strand (as squeezed between the rolling unit and the lock arrangement) is distributed over a wider contact area by flexion of the resilient material. This is done so for the dual purposes of both eliminating formation of weak spots in the line as well as for enhancing frictional grabbing of the line to eliminate slip of the locked line.
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