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