respectively carried by lower ends of the rods 98 and 100 as can best be seen in fig1 the rod 98 of the right cylinder 64 is shown in its full up position while the rod 100 of the left cylinder 66 is shown in its full down position thus it will be appreciated that by simultaneously connecting air pressure to the top of the piston 102 carried by the rod 98 and to the bottom of the piston 104 carried by the rod 100 while simultaneously venting the spaces below and above the pistons 102 and 104 respectively the rod 98 will move downwardly while the rod 101 moves upwardly thus effecting clockwise rotation of the upper and lower sprockets 46 and 60 and hence of the upper and lower shafts 36 and 50 a mandrel 118 in the form of a square plate has a centrally located hole passing therethrough and is welded to a forward end of the lower shaft 50 which is received in the hole whereby the mandrel rotates with the shaft a plurality of the threaded holes 120 are provided in the mandrel 118 and are arranged in a square pattern having the shaft 50 at its center interchangeable core handling attachments examples of which are described below are adapted to be bolted to the mandrel the rotation imparted to the mandrel 118 by actuation of the cylinders 64 and 66 is precisely controlled by a stop mechanism fig4 including a rotation limiting plate 122 mounted to a forward end of the upper shaft 36 for rotation therewith specifically.