stressed condition in other words within a total range of angular deflection of 45 degrees 22 5 degrees clockwise such as in the clockwise direction cw as shown in fig6 and 22 5 degrees counterclockwise relative to a relaxed unstressed state m the amount of angular deflection increases at a linear rate with respect to applied torque a preferred material for the sleeve member 20 is a thermoplastic polyamide such as u201c nylon 12 u201d which is readily moldable into the sleeve configuration illustrated the elongate slots 31 32 provide the desired level of elastic torsional deflection and fatigue resistance to this end the slots 31 32 are elongate lengthwise of the sleeve and define a series of elongate somewhat hour glass shaped strips of sleeve wall material between them the slots extend for a distance of less than about one half the overall length of the sleeve and more preferably they extend for less than about one quarter of the overall sleeve length preferably the sleeve has an overall tubular length of about 4 inches a diameter of about one inch and a wall thickness of about 0 060 inch a majority of the slots have a length of about one 1 inches and a maximum medial width of about 0 1 inch each of the slot side walls bows outwardly from opposite curved ends such.