An electric plug having a central signal shaft terminating in a tip, wherein {HEAD ~ the tip} has a substantially frustoconical nose, a convex annular shoulder centered at an axial distance of less than 0.120 inch from the front end of the tip, and {TAIL ~ a concave waist} having a radius of curvature greater than about 0.75 inch, defining the detent adjacent to the bulbous portion 
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An electric plug having a central signal shaft terminating in a tip , wherein { HEAD ~ the tip } has a substantially frustoconical nose , a convex annular shoulder centered at an axial distance of less than 0.120 inch from the front end of the tip , and { TAIL ~ a concave waist } having a radius of curvature greater than about 0.75 inch , defining the detent adjacent to the bulbous portion
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