I had a number of shelf brackets mounted on a wall, wanting to add three pieces of shelf on top. Unfortunately the brackets were a little bit off, so the shelves looked awful where they met. 3D-print to the rescue! These little shims, printed in 1 and 2 mm heights, were enough to align the shelves nicely.

The "v8" files fit the smallest and now out-of-production brackets of a common German type, while the "-20-" files fit the 20cm version of the same brackets. The OpenSCAD file can relatively easily be adjusted to fit other sizes.