This is a Gridfinity 3x1x3 module measuring B=125.5mm H=45mm D=125.5mm (external measurements) with stacking lip, using the parametric model made by InaniaEtVana https://www.printables.com/model/491143-parametric-gridfinity-bottoms-gridfinity-model-bas where i set the height to 42mm (couldn't resist and they fit perfectly in the drawer i made it for).
The author remixed this model.
.stl and .step files for a Gridfinity 3x1x3 box