Backbracket thumbscrew assembly

摘要

A thumbscrew apparatus for fastening a first device to a second device. In a first embodiment, the apparatus comprises a screw attached to the second device and a first cylinder screwed onto the screw for fastening the first device to the second device. The first cylinder has an outboard end with a one-way slot feature that allows a screwdriver to be used to loosen the first cylinder while inhibiting the use of the screwdriver to tighten the cylinder. In a second embodiment, the shaft of the screw has a first portion smaller in diameter than a second portion. The first portion also has a thread pitch smaller than that of the second portion. A second cylinder contained within the first cylinder is screwed onto the second portion of the shaft while the first cylinder is screwed onto the first portion. A pin is used to lock the first cylinder to the second cylinder such that both cylinders are turned at the same revolution. However, since the pitch of the second portion of the shaft is greater than that of the first portion, the second cylinder moves faster along the axis of the screw than the first cylinder. Hence, when both cylinders are being turned in the loosening direction, the second cylinder pushes the screwdriver out of the one-way slot of the outboard end of the first cylinder before the first cylinder reaches the end of its travel.