| 摘要 |
A single strip member is provided constructed of non-elastic rigid material having minimal flexive properties and the strip member is constructed in the form of an arcuate band of an angular extent greater than 360 DEG with at least slightly overlapped ends. Each of the ends is in the form of a circumferentially extending channel member with one of the channel members being more narrow than the other channel member and at least partially length wise telescoped therein. The side flanges of one of the channel members have an overcenter swingable actuating lever pivotally supported therefrom for swinging in the plane of the arcuate strip member and an overcenter positionable portion of the lever has one end of a stiff expansion spring anchored relative thereto while the other end of the expansion spring is anchored relative to the other channel member.
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