I have 9 of these Twinlock desk trays in my study (https://www.takealot.com/twinlock-desk-tray-red-2-trays-and-4-risers/PLID28028793), however the risers that came with them are at best very flimsy and the trays are not very solid/sturdy once you start filling them up with paperwork.
The set of two trays also only comes with 4 risers, so you are limited to two stacked trays only - I wanted 3 stacked trays to fit my shelf spacing, so I designed these risers to allow me to do this; although printed form PLA, they are much more rigid than the originals, so I ended up replacing all the risers with this printed version - the trays are now very sturdy and don't rock from side to side when full.
Probably by absolute fluke, the design was sized from an original riser, however the printed dimensions are about 0.5mm larger than the original, allowing for a nice tight fit in the lower riser sockets, which certainly helps with the rigidity!
These were designed specifically for the Twinlock series trays shown in the above link, but I'm sure they could fit other brands/models if the riser slots were similar or the STL dimensions were tweaked - the Sketchup file is included should you wish to make your own changes.
The dimension are:
Length = 97mm - gives a tray spacing of 120mm total (bottom tray to bottom of next tray)
Width = 23mm
Height = 5.2mm
You can change the length of the risers by stretching the length in your slicer to what you require, but I would not go beyond 150mm unless you print in ABS or PETG - so if you want your trays to be further apart, adjust the length!