the outer frame side plate 33 the motor 45 has an output shaft not shown which projects through a complementary opening in the side plate 42 and is fixed to a drive gear 46 disposed between the plates 41 and 42 see fig2 the rear ends of the side plates 41 and 42 are apertured to receive therethrough the rear bolt 35 and its associated spacer this inner spacer being surrounded with outer spacers to space the plates 41 and 42 of the inner frame 40 the forward ends of the side plates 41 and 42 are provided with downwardly opening notches 47 dimensioned to fit over the sleeve 11 the inner frame 40 is pivotally movable about the axis of the rear bolt 35 between an open condition not show to allow insertion of the sleeve 11 into the notches 37 of the outer frame 31 and a closed or engaged condition illustrated in the drawings dropped down over the sleeve 11 for cooperation with the outer frame 31 to retain the drive unit 30 in a drive configuration coupled to the sleeve 11 in this drive configuration the drive gear 46 is disposed in meshing engagement with the driven gear 12 of the cable tightener 10 in order to facilitate manipulation of the drive unit 30 it is provided with an.