| 摘要 |
An eraser advancing mechanism for a mechanical pencil has a pair of nested screws within a barrel. A second screw, with outwardly directed threads, extends through a conduit in a first screw that includes outwardly directed threads and a thread in the conduit meshing with the threads of the second screw. An eraser ferrule includes a thread that meshes with the outwardly directed threads of the first screw. The ferrule includes a knob serving to drive rotation of the eraser ferrule, and hence the first screw. The first screw includes a head with a profile that complements the inner profile of the barrel. Rotation of the first screw causes rotation of the barrel and serves to create a counter-rotation of the second screw, leading to axial movement of the second screw relative to the first screw.
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