sleeve 39 the sleeve 39 is slideably mounted on the shaft 11 and is rotationally locked thereto by means of a key 41 protruding from the shaft 11 and a slot 42 formed in the sleeve 39 the key 41 is a cylindrical pin pressed into a matching bore in the shaft 11 as shown in fig7 the slot 42 in the sleeve 39 extends axially to permit the sleeve to slide upon the shaft 11 while being rotationally locked thereto the shaft 11 is formed with a threaded lift end portion 44 of reduced diameter as shown in fig2 a bore 45 extends axially from the left end of the shaft 11 a rod 46 is positioned in and extends from the bore 45 the axial position of the rod 46 within the bore 45 is controlled by a hand wheel 47 the hand wheel 47 has a hand ring 49 attached to a hub 50 by spokes 51 a threaded ring 52 engaging the shaft portion 44 is bolted to the inner end of the hub 50 a locking nut 57 is also provided on the shaft portion 44 referring now particularly to fig4 and 5 the shaft 11 is formed with a diametrically extending slot.