accomplished by an over center linkage 35 comprising a pair of oppositely disposed links 36 pivotally connected to the lower jaw 24 at 37 and at 38 to a jaw operating lever 40 as shown in fig6 the lever 40 is pivoted at its lower end on a pin 41 which slip fits into bores 42 in spaced lugs 43 integral with housing 20 the pin 41 has a slotted head as shown at 44 and the center portion of pin 41 is eccentric as shown at 45 this arrangement is such that by rotational adjustment of the pin 41 the position of the pivotal center of handle 40 may be adjusted so that it can be moved to a position slightly over or under center as shown in fig3 and thus effect a clamping of the lower jaw 24 against an over or undersized workpiece held against the upper jaw 23 a three piece wedge and screw assembly shown in detail in fig1 comprising a cap screw 47 having an 34 allen 34 hex head 48 and threaded through a nut 49 which may be tightened or loosened to cause wedges 50 to bear against or free pin 41 on a relieved diameter to hold the pin in any adjusted position a stop lug 52 of fig6 secured to the upper jaw 23 at 53 lies in the.