Countersunk screw that is invisible when fitted and cannot be unscrewed when fitted - includes gripping member which is separated from conical part and situated in axial extension of screw beyond conical part,this extension meant to shear off after certain torque limit

摘要

The countersunk head screw consists of a threaded part (11) and a conical section (12) forming its head. Joined to this head (12) is a drive nut (13) which is gripped by the tool used for driving in the screw. The head of the screw (12) and the drive nut (13) are joined by a thinned part (14) which is at its narrowest (16) where it joins the flat part of the screw head (12). In fixing of the screw, once it is driven home, any extra torque on the drive nut (13) shears the joining part (14) at its narrowest section (16) flush with the head (12). Use/Advantage - A countersunk headed screw which gives an invisible flush appearance when screwed home which cannot be unscrewed by any of the conventional methods.