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SCREW-TYPE MECHANISM WITH TUMBLER HALF-NUTS

Half-nut link 2 slides along fixed guide a and can be turned about the axis of the guide so that its half-nuts engage screw 1 or screw 3. When the corresponding half-nut of link 2 is engaged to screw 1 having right-hand thread, link 2 slides in one direction along guide a. This direction can be reversed by disengaging link 2 from link 1 and bringing the other half-nut into engagement with screw 3 …