similar to the operative connection between the first crank means 50 and the first adjustment housing 26 for ease of fabrication the right hand portion of the central pipe 16 is provided with diametrically opposed elongated slots 62 that are 90 degrees out of alignment and spaced longitudinally of slots 52 the second adjustment housing 28 is provided with tabs 63 attached thereto and arranged in a manner similar to the arrangement of the tabs 34 relative to the first adjustment housing 26 a series of link members 64 pivotally interconnect each of the tabs 63 to a corresponding apertured tab 66 attached to the end portion 68 of the corresponding peripheral arm 24 adjacent radially extending arms 20 it is now obvious that the first crank means 50 can be operated to adjust the circumference of the mandrel 10 at its axial end portion adjacent the radially extending arms 18 independently of the operation of the second crank means 60 to adjust the circumference of the mandrel 10 at its axial end portion adjacent the radially extending arms 20 therefore it is possible with the apparatus of the illustrative embodiment to adjust the circumferential length of either axial end of.