The definition corresponding to this phrase is a cylindrical mechanical piece, of metal with spiral body and head of different formats, inside which there is a hexagonal hollow, which by means of a force that exerts twisting on its head with an Allen key can be introduced threaded in a hole to your size or also pass through pieces and attach to a nut. The measurement of the Allen screws is made in millimeters, differentiating well from the whitworth that use measures in inches

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拍攝者： Luland2013