A spreader plate assembly intended for use with an arbor carriage includes two congruent rectangular plates, one overlying the other. Each plate has two spaced apart notches disposed on one long side and a circular bore near one of the short sides. The plates are connected in mirror-reversed position relative to one another by a fastener inserted through the bore in each plates, thereby pivotably connecting them and enabling them to be moved relative to one another between an open and a closed position. In the closed position, the two spaced apart notches of each plate straddle two spaced apart vertical rods of the arbor carriage.