PURPOSE: To provide a rigid adjustable support riser for vertically stacking letter trays.

CONSTITUTION: Since an upper attachment socket comprising finger flanges 30, 32, 42 for securing to a lower letter tray and a riser body having the upper attachment socket 12 is provided with an elongated ovular shape, an upper tray can be selectively placed in either a forward or a rearward socket location relative to the upper end of the riser. A reinforcement flange is provided to extend along each cantilevered inward finger, whereby adding rigidity and strength to the lower attachment point.