to and translatable with reciprocable base member 8 as well as being fixed in relation to one another plate like member 24 which forms the movable portion of gripping means 18 is positioned between plate like member 20 and 22 fig9 illustrates the gripping means 18 in a 34 gripping 34 position which is described in greater detail hereinbelow as can be most clearly seen in fig1 upper plate like member 20 is spaced from lower plate like member 22 by a pair of lateral spacer bars 21 which also form part of the stationary portion 17 spacer bars 21 serve as lateral guides for plate like member 24 as it reciprocates relative to the stationary portion 17 the operation of which is described hereinbelow plate like members 20 22 and spacer bars 21 are each provided with a plurality of holes 23 which are alignable with one another to receive a plurality of preferably removable fasteners 25 such as screws or bolts for rigidly fastening plate like members 20 22 to one another and also to spacer bars 21 with such a construction plate like member 24 is constrained by the inner surfaces of plate like members 20 22 and the inner surfaces of spacer bars 21 to reciprocate in a.