Two of the edges are sharp 90 degree edges for inner corners and crevices, while the other two edges are gently filleted around a concave inner slope for sanding rounded surfaces.
The .stl file itself is a solid object, but to get the honeycomb effect in the picture, print the part with:
Supports are not needed, just print the part on it's side.
Scale the model as large or as small as you need for your sanding requirements. Object defaults are 60mm L x 30mm H x 10mm or 20mm D
The author marked this model as their own original creation.