to holes not shown in flanges 24 of the arm 22 nuts 62 prevent the bolts from sliding through the holes in the flanges a washer 64 is interposed between the nut 62 and flange 24 springs 66 encompass the bolt 60 the upper portion of the springs 66 abut against the top of the box assembly 26 which in turn abuts the flanges 24 of the arm 22 the lower portion of the springs 66 abut against the nut 68 attachment of the bolt 60 to the upper platen assembly 20 will now be shown with reference to fig6 as just indicated the spring 66 not shown in this view abuts nut 68 the bolt 60 threadably engages the plate 70 which comprises the upper platen assembly 20 and is locked thereto by nut 72 the pressure exerted by the platens may also be adjusted by varying the position of the nut 62 on the bolt 60 thus adjusting the force exerted by the spring 66 the upper and lower platen assemblies 20 and 18 are thus supported in a manner which assures substantial uniformity of pressure distribution when they are engaged any misalignment between the two platens is inherently compensated for due to the floating or spring mounting.