position engaging the printed circuit board support 5 at a point within the cut out 15 in this manner the stop mechanism 90 may be utilized to control the movement of selected printed circuit board supports 5 along the conveyor path in operation one of a plurality of spacers 50 see fig2 having different thicknesses is selected depending upon the thickness profile of the printed circuit board 80 engaged by the pair of conveyor rails 64 more specifically the spacer 50 having a thickness most suitable for optimum supportive engagement of the printed circuit board 80 by the printed circuit board support 5 is selected the selected spacer 50 is installed by extending or positioning the respective projections 56 into the corresponding recesses 54 the upper spacer surface 58 of the selected spacer 50 is then utilized to engage the printed circuit board 80 within the operating envelope of the pick and place machine 76 alternatively the spacer 50 may be eliminated and the base extension assembly 20 may be arranged to define a variable extension assembly height dimension a as discussed herein with reference to fig3 and the height dimension of the base extension assembly 20 may be varied as a function of a thickness profile of the printed circuit board 80 in which case the upper surface 12 will engage the printed circuit board 80 it is contemplated that the variable height base extension assembly 20 and the spacers 50 may be utilized in a cooperative.