Abstract: A sucker rod including a sucker rod body (122); a transition section (125) having an outer surface disposed circumferentially around the longitudinal axis of the transition section, the outer surface having a longitudinal profile comprising a continuous curve beginning at the cylindrical outer surface of the rod body and having a concave curved portion having a radius (RA) and a convex curved portion having a radius (RB), wherein RB is less than RA and a diameter of the transition section measured transverse to the longitudinal axis (AA) is continuously increasing with distance from the outer surface of the rod; a wrench square section (127) having at least four wrench flats (124); a pin shoulder section (128) having a pin shoulder face (126) adapted to contact an end of a coupling (117) the pin shoulder face having an outer diameter (DF); and a threaded pin connection section (129) having male threads.