end of element 13 extending axially longitudinal in element 13 end cap 27 is configured with radially inward extending distal end face flange portion 28 disposed in sliding contact with the peripheral face of distal end portion 21 of element 13 end caps 17 and 27 retain assembly of drive shaft 10 intact helical compression spring 30 is disposed peripherally around proximal end portion 21 of driver element 13 between shoulder 24 of element 13 and flange portion 28 of end cap 27 flexible sleeve 20 is fixedly secured to the inner peripheral surfaces of end caps 17 and 27 it is kept tautly drawn by tensioning action of spring 30 acting through tightly coupled nesting components of drive shaft 10 disposed intermediate the two ends of the shaft spring 30 forcibly bears on shoulder 24 of element 13 and flange portion 28 of end cap 27 and resiliently adjusts by operably expanding or contracting in response to curvilinear flexing of drive shaft 10 during use in the embodiment of invention of fig2 driver end element 13 u2032 differs from similar element 13 of fig1 and 3 by comprising two components i e core piece 13 u2033 and socket piece 31 u2032 the two latter components are unitarily affixed to provide the same configuration as element 13 of fig1 and 3 but allows for alternative ways of manufacturing components whether by forging casting machining press fitting or other known processes in fig2 shoulder 24 u2032 is configured as an integral band configured portion which increases the outer diameter of.