sleeve 15 having two tabs 18 and 21 in fig3 which mate with slots 24 and 26 in the actuating arm 6 in fig1 the tabs 18 and 21 inhibit rotation of the locking sleeve 15 with respect to the arm 6 since the arm 6 is keyed to the shaft 3 by key 25 and keyway 25a the rotation of the locking sleeve 15 with respect to the shaft 3 is inhibited the base region 27 of the nut 12 is cylindrical however an upper region 27a in fig3 of the locking sleeve 15 is generally elliptical as shown in fig2 while a base region 27b in fig3 is generally circular further the locking sleeve 15 contains a flare 30 in fig3 which cooperates with the bottom edge 33 in fig1 of the nut 12 to deform the locking sleeve from its original elliptical shape into a shape more conforming to the cylindrical shape of the base 27 of the nut 12 thus the sleeve 15 applies a frictional locking force which is largest at points 36 and 39 which are diametrically opposed in fig2 and which decreases to the lower values at points 42 and 44 also diametrically opposed characterized another way the present invention includes a circular base region 28 in fig3 a sleeve extends upward from the base 28 and includes two regions a lower region 27b near the base 28 which is cylindrical and an upper region 27a near the flare 30 which is elliptical the transformation from cylindrical to elliptical causes the sleeve to slope inward toward axis 50 in the cross section viewed in the direction of arrows 3 3 in fig2.