A susceptible subject to be cut having a threaded shank adapted for engagement with a threaded bore and a head portion (25) formed for engagement with a turning tool, the shank being formed with a series of areas weakened separate axially (21, 22, 23) defining a series of shear planes, wherein the weakenings (21, 22, 23) are formed such that the applied torque necessary to cause the stem is cut gradually increases from the cutting plane further from the part of the head (25) to the plane closer to the part of the head section (25), wherein the weakenings (21, 22, 23) comprise holes , grooves or slits formed in the shank, wherein the radius at the bottom of the holes, grooves or slits varies to produce or contribute to the said increase of torque cutting, and that the weakenings ( 21, 22, 23) comprise annular grooves, the depth of the grooves substantially the same from the farthest part of the head (25) to the nearest part of the head (25).
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