I found myself more than once needing a simple box. Every time I would remodel it in Fusion 360. However, I got tired of basically doing the same project over and over again so I created this parametric box.

I attached a 30mm x 30mm x 3mm internal dimensions box STL as an example and the picture is of the baby 10mm x 10mm x 3mm internal dimensions box, the smallest you can go.

The model:

It is a simple box where you can choose the internal size. It is easy to print as there are no overhangs or bridges. 

Just pay attention to the top of the grip as it is a fin wall, a single extrusion, so if you have a large diameter nozzle with a large print width, it might not print right.

Parameters:

To access the parameters, download and open the F3D file, in the Solid menu, expand Modify and select Change Parameters.

All user-selectable parameters are flagged as favourites, and the minimum values are set as Comments. 

Attention: Fusion 360 sometimes gets lost in the calculation when increasing or decreasing the Internal box size in large chunks (e.g. going from 100mm to 10mm). If that happens, try reducing it in 10mm increments (e.g. if you want to go from 100mm to 20mm, reduce it to 90mm, 80mm, 70mm, 60mm, 50mm, etc, until reaching out 20mm).