TAMPER-RESISTANT ROTARY FASTENERS AND TOOLS FOR USE WITH THEM

摘要

A tamper-resistant threaded fastener (1) comprises a head (2) and shank (3) having a threaded part (4), the head having a circular recess (5) which is coaxial with the screw threading (4) and, at the bottom of the said recess (5) a further circular recess (6) which is of lesser diameter than the first recess and has a common tangent therewith. A tool for use with such a fastener is characterised by a cylindrical shank portion having at its end a cylindrical extension which is of lesser diameter than the shank portion and is eccentric relative thereto.